| Message ID | 20121024052351.GB21714@thunk.org |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Wed, 24 Oct 2012, Theodore Ts'o wrote: > Journal flushes outside of an unmount does > happen as part of online resizing, the FIBMAP ioctl, or when the file > system is frozen. But it didn't sound like Toralf or Nix was using > any of those features. (Toralf, Nix, please correct me if my > assumptions here is wrong). I believe it also happens at swapon of a swapfile on the filesystem. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 24 Oct 2012, Theodore Ts'o stated: > Journal flushes outside of an unmount does > happen as part of online resizing, the FIBMAP ioctl, or when the file > system is frozen. But it didn't sound like Toralf or Nix was using > any of those features. Quite so -- the corrupted filesystems have space reserved for resizing, and one of them has been resized, years ago, but I haven't resized either of them with this kernel, or with any kernel numbered 3.x for that matter. > Toralf, Nix, if you could try applying this patch (at the end of this > message), and let me know how and when the WARN_ON triggers, and if it > does, please send the empty_bug_workaround plus the WARN_ON(1) report. > I know about the case where a file system is mounted and then > immediately unmounted, but we don't think that's the problematic case. > If you see any other cases where WARN_ON is triggering, it would be > really good to know.... I'll give it a test later today, after another backup has finished. Daily backups are normally overkill, but I don't think they are right now.
On 24 Oct 2012, Hugh Dickins verbalised: > On Wed, 24 Oct 2012, Theodore Ts'o wrote: >> Journal flushes outside of an unmount does >> happen as part of online resizing, the FIBMAP ioctl, or when the file >> system is frozen. But it didn't sound like Toralf or Nix was using >> any of those features. (Toralf, Nix, please correct me if my >> assumptions here is wrong). > > I believe it also happens at swapon of a swapfile on the filesystem. I'm not using swapfiles, only swap partitions (on separate LVM LVs). So that's not it either.
On 10/24/2012 12:23 AM, Theodore Ts'o wrote: > On Tue, Oct 23, 2012 at 11:27:09PM -0500, Eric Sandeen wrote: >> >> Ok, fair enough. If the BBU is working, nobarrier is ok; I don't trust >> journal_async_commit, but that doesn't mean this isn't a regression. > > Note that Toralf has reported almost exactly the same set of symptoms, > but he's using an external USB stick --- and as far as I know he > wasn't using nobarrier and/or the journal_async_commit. Toralf, can > you confirm what, if any, mount options you were using when you saw > it. > > I've been looking at this some more, and there's one other thing that > the short circuit code does, which is neglects setting the > JBD2_FLUSHED flag, which is used by the commit code to know when it > needs to reset the s_start fields in the superblock when we make our > next commit. However, this would only happen if the short circuit > code is getting hit some time other than when the file system is > getting unmounted --- and that's what Eric and I can't figure out how > it might be happening. Journal flushes outside of an unmount does > happen as part of online resizing, the FIBMAP ioctl, or when the file > system is frozen. But it didn't sound like Toralf or Nix was using > any of those features. (Toralf, Nix, please correct me if my > assumptions here is wrong). If I freeze w/ anything in the log, then s_start !=0 and we proceed normally. If I re-freeze w/o anything in the log, it's already set to FLUSHED (which makes sense) so not re-setting it doesn't matter. So I don't see that that's an issue. As for FIBMAP I think we only do journal_flush if it's data=journal. In other news, Phoronix is on the case, so expect escalating freakouts ;) -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 24 Oct 2012, Theodore Ts'o spake thusly: > Toralf, Nix, if you could try applying this patch (at the end of this > message), and let me know how and when the WARN_ON triggers, and if it > does, please send the empty_bug_workaround plus the WARN_ON(1) report. > I know about the case where a file system is mounted and then > immediately unmounted, but we don't think that's the problematic case. > If you see any other cases where WARN_ON is triggering, it would be > really good to know.... Confirmed, it triggers. Traceback below. But first, a rather lengthy apology: I did indeed forget something unusual about my system. In my defence, this is a change I made to my shutdown scripts many years ago, when umount -l was first introduced (early 2000s? something like that). So it's not surprising I forgot about it until I needed to add sleeps to it to capture the tracebacks below. It is really ugly. You may need a sick bag. In brief: some of my filesystems will sometimes be uncleanly unmounted and experience journal replay even on clean shutdowns, and which it is will vary unpredictably. Some of my machines have fairly intricate webs of NFS-mounted and non-NFS-mounted filesystems, and I expect them all to reboot successfully if commanded remotely, because sometimes I'm hundreds of miles away when I do it and can hardly hit the reset button. Unfortunately, if I have a mount structure like this: /usr local /usr/foo NFS-mounted (may be loopback-NFS-mounted) /usr/foo/bar local and /usr/foo is down, any attempt to umount /usr/foo/bar will hang indefinitely. Worse yet, if I umount the nfs filesystem, the local fs isn't going to be reachable either -- but umounting nfs filesystems has to happen first so I can killall everything (which would include e.g. rpc.statd and rpc.nfsd) in order to free up the local filesystems for umount. The only way I could see to fix this is to umount -l everything rather than umounting it (sure, I could do some sort of NFS-versus-non-NFS analysis and only do this to some filesystems, but testing this complexity for the -- for me -- rare case of system shutdown was too annoying to consider). I consider a hang on shutdown much worse than an occasional unclean umount, because all my filesystems are journalled so journal recovery will make everything quite happy. So I do sync umount -a -l -t nfs & sleep 2 killall5 -15 killall5 -9 exportfs -ua quotaoff -a swapoff -a LANG=C sort -r -k 2 /proc/mounts | \ (DIRS="" while read DEV DIR TYPE REST; do case "$DIR" in /|/proc|/dev|/proc/*|/sys) continue;; # Ignoring virtual file systems needed later esac case $TYPE in proc|procfs|sysfs|usbfs|usbdevfs|devpts) continue;; # Ignoring non-tmpfs virtual file systems esac DIRS="$DIRS $DIR" done umount -l -r -d $DIRS) # rely on mount's toposort sleep 2 The net effect of this being to cleanly umount everything whose mount points are reachable and which unmounts cleanly in less than a couple of seconds, and to leave the rest mounted and let journal recovery handle them. This is clearly really horrible -- I'd far prefer to say 'sleep until filesystems have finished doing I/O' or better have mount just not return from mount(8) unless that is true. But this isn't available, and even it was some fses would still be left to journal recovery, so I kludged it -- and then forgot about doing anything to improve the situation for many years. So, the net effect of this is that normally I get no journal recovery on anything at all -- but sometimes, if umounting takes longer than a few seconds, I reboot with not everything unmounted, and journal recovery kicks in on reboot. My post-test fscks this time suggest that only when journal recovery kicks in after rebooting out of 2.6.3 do I see corruption. So this is indeed an unclean shutdown journal-replay situation: it just happens that I routinely have one or two fses uncleanly unmounted when all the rest are cleanly unmounted. This perhaps explains the scattershot nature of the corruption I see, and why most of my ext4 filesystems get off scot-free. I'll wait for a minute until you're finished projectile-vomiting. (And if you have suggestions for making the case of nested local/rewmote filesystems work without rebooting while umounts may still be in progress, or even better suggestions to allow me to umount mounts that happen to be mounted below NFS-mounted mounts with dead or nonresponsive NFS server, I'd be glad to hear them! Distros appear to take the opposite tack, and prefer to simply lock up forever waiting for a nonresponsive NFS server in this situation. I could never accept that.) [...] OK. That umount of local filesystems sprayed your added empty bug workaround and WARN_ONs so many times that nearly all of them scrolled off the screen -- and because syslogd was dead by now and this is where my netconsole logs go, they're lost. I suspect every single umounted filesystem sprayed one of these (and this happened long before any reboot-before-we're-done). But I did the old trick of camera-capturing the last one (which was probably /boot, which has never got corrupted because I hardly ever write anything to it at all). I hope it's more useful than nothing. (I can rearrange things to umount /var last, and try again, if you think that a specific warning from an fs known to get corrupted is especially likely to be valuable.) So I see, for one umount at least (and the chunk of the previous one that scrolled offscreen is consistent with this): jbd2_mark_journal_empty bug workaround (21218, 21219) [obscured by light] at fs/jbd2/journal.c:1364 jbd2_mark_journal_empty+06c/0xbd ... [addresses omitted for sanity: traceback only] warn_slowpath_common+0x83/0x9b warn_slowpath_null+0x1a/0x1c jbd2_mark_journal_empty+06c/0xbd jbd2_journal_destroy+0x183/0x20c ? abort_exclusive_wait+0x8e/0x8e ext4_put_super+0x6c/0x316 ? evict_inodes+0xe6/0xf1 generic_shutdown_super+0x59/0xd1 ? free_vfsmnt+0x18/0x3c kill_block_super+0x27/0x6a deactivate_locked_super+0x26/0x57 deactivate_super+0x3f/0x43 mntput_no_expire+0x134/0x13c sys_umount+0x308/0x33a system_call_fastpath+0x16/0x1b -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 24 Oct 2012, nix@esperi.org.uk uttered the following: > So, the net effect of this is that normally I get no journal recovery on > anything at all -- but sometimes, if umounting takes longer than a few > seconds, I reboot with not everything unmounted, and journal recovery > kicks in on reboot. My post-test fscks this time suggest that only when > journal recovery kicks in after rebooting out of 2.6.3 do I see > corruption. So this is indeed an unclean shutdown journal-replay > situation: it just happens that I routinely have one or two fses > uncleanly unmounted when all the rest are cleanly unmounted. This > perhaps explains the scattershot nature of the corruption I see, and why > most of my ext4 filesystems get off scot-free. Note that two umounts are not required: fsck found corruption on /var after a single boot+shutdown round in 3.6.3+this patch. (It did do a journal replay on /var first.)
On 10/24/2012 02:49 PM, Nix wrote: > On 24 Oct 2012, Theodore Ts'o spake thusly: >> Toralf, Nix, if you could try applying this patch (at the end of this >> message), and let me know how and when the WARN_ON triggers, and if it >> does, please send the empty_bug_workaround plus the WARN_ON(1) report. >> I know about the case where a file system is mounted and then >> immediately unmounted, but we don't think that's the problematic case. >> If you see any other cases where WARN_ON is triggering, it would be >> really good to know.... > > Confirmed, it triggers. Traceback below. > <giant snip> The warn on triggers, but I can't tell - did the corruption still occur with Ted's patch? -Eric > > OK. That umount of local filesystems sprayed your added > empty bug workaround and WARN_ONs so many times that nearly all of them > scrolled off the screen -- and because syslogd was dead by now and this > is where my netconsole logs go, they're lost. I suspect every single > umounted filesystem sprayed one of these (and this happened long before > any reboot-before-we're-done). > > But I did the old trick of camera-capturing the last one (which was > probably /boot, which has never got corrupted because I hardly ever > write anything to it at all). I hope it's more useful than nothing. (I > can rearrange things to umount /var last, and try again, if you think > that a specific warning from an fs known to get corrupted is especially > likely to be valuable.) > > So I see, for one umount at least (and the chunk of the previous one > that scrolled offscreen is consistent with this): > > jbd2_mark_journal_empty bug workaround (21218, 21219) > [obscured by light] at fs/jbd2/journal.c:1364 jbd2_mark_journal_empty+06c/0xbd > ... > [addresses omitted for sanity: traceback only] > warn_slowpath_common+0x83/0x9b > warn_slowpath_null+0x1a/0x1c > jbd2_mark_journal_empty+06c/0xbd > jbd2_journal_destroy+0x183/0x20c > ? abort_exclusive_wait+0x8e/0x8e > ext4_put_super+0x6c/0x316 > ? evict_inodes+0xe6/0xf1 > generic_shutdown_super+0x59/0xd1 > ? free_vfsmnt+0x18/0x3c > kill_block_super+0x27/0x6a > deactivate_locked_super+0x26/0x57 > deactivate_super+0x3f/0x43 > mntput_no_expire+0x134/0x13c > sys_umount+0x308/0x33a > system_call_fastpath+0x16/0x1b -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 24 Oct 2012, Eric Sandeen uttered the following: > On 10/24/2012 02:49 PM, Nix wrote: >> On 24 Oct 2012, Theodore Ts'o spake thusly: >>> Toralf, Nix, if you could try applying this patch (at the end of this >>> message), and let me know how and when the WARN_ON triggers, and if it >>> does, please send the empty_bug_workaround plus the WARN_ON(1) report. >>> I know about the case where a file system is mounted and then >>> immediately unmounted, but we don't think that's the problematic case. >>> If you see any other cases where WARN_ON is triggering, it would be >>> really good to know.... >> >> Confirmed, it triggers. Traceback below. > > <giant snip> > > The warn on triggers, but I can't tell - did the corruption still occur > with Ted's patch? Yes. I fscked the filesystems in 3.6.1 after rebooting: /var had a journal replay, and the usual varieties of corruption (free space bitmap problems and multiply-claimed blocks). (The other filesystems for which the warning triggered had neither a journal replay nor corruption. At least one of them, /home, likely had a few writes but not enough to cause a journal wrap.) I note that the warning may well *not* have triggered for /var: if the reason it had a journal replay was simply that it was still in use by something that hadn't died, the umount -l will have avoided doing a full umount for that filesystem alone. Also, the corrupted filesystem was mounted in 3.6.3 exactly once. Multiple umounts are not necessary, but an unclean umount apparently is.
On 24 Oct 2012, nix@esperi.org.uk spake thusly: > So, the net effect of this is that normally I get no journal recovery on > anything at all -- but sometimes, if umounting takes longer than a few > seconds, I reboot with not everything unmounted, and journal recovery > kicks in on reboot. It occurs to me that it is possible that this bug hits only those filesystems for which a umount has started but been unable to complete. If so, this is a relatively rare and unimportant bug which probably hits only me and users of slow removable filesystems in the whole world...
On Wed, Oct 24, 2012 at 09:45:47PM +0100, Nix wrote: > > It occurs to me that it is possible that this bug hits only those > filesystems for which a umount has started but been unable to complete. > If so, this is a relatively rare and unimportant bug which probably hits > only me and users of slow removable filesystems in the whole world... Can you verify this? Does the bug show up if you just hit the power switch while the system is booted? How about changing the "sleep 2" to "sleep 0.5"? (Feel free to unmount your other partitions, and just leave a test file system mounted to minimize the chances that you lose partitions that require hours and hours to restore...) If you can get a very reliable repro, we might have to ask you to try the following experiments: 0) Make sure the reliable repro does _not_ work with 3.6.1 booted 1) Try a 3.6.2 kernel 2) (If the problem shows up above) try a 3.6.2 kernel with 14b4ed2 reverted 3) (If the problem shows up above) try a 3.6.2 kernel with all of ext4 related patches reverted: 92b7722 ext4: fix mtime update in nodelalloc mode 34414b2 ext4: fix fdatasync() for files with only i_size changes 12ebdf0 ext4: always set i_op in ext4_mknod() 22a5672 ext4: online defrag is not supported for journaled files ba57d9e ext4: move_extent code cleanup 2fdb112 ext4: fix crash when accessing /proc/mounts concurrently 1638f1f ext4: fix potential deadlock in ext4_nonda_switch() 5018ddd ext4: avoid duplicate writes of the backup bg descriptor blocks 256ae46 ext4: don't copy non-existent gdt blocks when resizing 416a688 ext4: ignore last group w/o enough space when resizing instead of BUG'ing 14b4ed2 jbd2: don't write superblock when if its empty 4) (If the problem still shows up) then we may need to do a full bisect to figure out what is going on.... - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 24 Oct 2012, Theodore Ts'o verbalised: > On Wed, Oct 24, 2012 at 09:45:47PM +0100, Nix wrote: >> >> It occurs to me that it is possible that this bug hits only those >> filesystems for which a umount has started but been unable to complete. >> If so, this is a relatively rare and unimportant bug which probably hits >> only me and users of slow removable filesystems in the whole world... > > Can you verify this? Does the bug show up if you just hit the power > switch while the system is booted? Verified! You do indeed need to do passing strange things to trigger this bug -- not surprising, really, or everyone and his dog would have reported it by now. As it is, I'm sorry this hit slashdot, because it reflects unnecessarily badly on a filesystem that is experiencing problems only when people do rather insane things to it. > How about changing the "sleep 2" to "sleep 0.5"? I tried the following: - /sbin/reboot -f of running system -> Journal replay, no problems other than the expected free block count problems. This is not such a severe problem after all! - Normal shutdown, but a 60 second pause after lazy umount, more than long enough for all umounts to proceed to termination -> no corruption, but curiously /home experienced a journal replay before being fscked, even though a cat of /proc/mounts after umounting revealed that the only mounted filesystem was /, read-only, so /home should have been clean - Normal shutdown, a 60 second pause after lazy umount of everything other than /var, and then a umount of /var the instant before reboot, no sleep at all -> massive corruption just as seen before. Unfortunately, the massive corruption in the last testcase was seen in 3.6.1 as well as 3.6.3: it appears that the only effect that superblock change had in 3.6.3 was to make this problem easier to hit, and that the bug itself was introduced probably somewhere between 3.5 and 3.6 (though I only rebooted 3.5.x twice, and it's rare enough before 3.6.[23], at ~1/20 boots, that it may have been present for longer and I never noticed). So the problem is caused by rebooting or powering off or disconnecting the device *while* umounting a filesystem with a dirty journal, and might have been introduced by I/O scheduler changes or who knows what other changes, not just ext4 changes, since the order of block writes by umount is clearly at issue. Even though my own system relies on the possibility of rebooting during umount to reboot reliably, I'd be inclined to say 'not a bug, don't do that then' -- except that this renders it unreliable to use umount -l to unmount all the filesystems you can, skipping those that are not reachable due to having unresponsive servers in the way. As far as I can tell, there is *no* way to tell when a lazy umount has completed, except perhaps for polling /proc/mounts: and there is no way at all to tell when a lazy umount switches from 'waiting for the last process to stop using me, you can reboot without incident' to 'doing umount, rebooting is disastrous'. And unfortunately I want to reboot if we're in the former state, but not in the latter. (It also makes it unreliable to use ext4 on devices like USB sticks that might suddenly get disconnected during a umount.) Further, it seems to me that this makes it dangerous to ever use umount -l at all, even during normal system operation, since the real umount might only start when all processes are killed at system shutdown, and the reboot could well kick in before the umount has finished. It also appears impossible for me to reliably shut my system down, though a 60s timeout after lazy umount and before reboot is likely to work in all but the most pathological of cases (where a downed NFS server comes up at just the wrong instant): it is clear that the previous 5s timeout eventually became insufficient simply because of the amount of time it can take to do a umount on today's larger filesystems. Truly, my joy is unbounded :( > 0) Make sure the reliable repro does _not_ work with 3.6.1 booted Oh dear. Sorry :((( I can try to bisect this and track down which kernel release it appeared in -- if it isn't expected behaviour, of course, which is perfectly possible: rebooting during a umount is at best questionable. But I can't do anything that lengthy before the weekend, I'm afraid.
On 25 Oct 2012, nix@esperi.org.uk said: > Even though my own system relies on the possibility of rebooting during > umount to reboot reliably, I'd be inclined to say 'not a bug, don't do > that then' -- except that this renders it unreliable to use umount -l to > unmount all the filesystems you can, skipping those that are not > reachable due to having unresponsive servers in the way. It's worse than that. If you're using filesystem namespaces, how can *any* shell script loop, or anything in userspace, reliably unmount all filesystems before reboot? It seems to me this is impossible. There is no process that necessarily has access to all namespaces, and when you bring PID namespaces into the picture there is no process that can even kill all userspace processes in order to zap their filesystems. I suspect we need a new blocking 'umountall' syscall and a command that calls it, which umounts everything it can in every filesystem namespace it can, skipping those that are (unreachable?) network mounts, and returns only when everything is done. (Possibly it should first kill every process it sees in every PID namespace other than that of the caller, too.) Then shutdown scripts can just call this, and get the right behaviour immediately.
On Thu, Oct 25, 2012 at 12:27:02AM +0100, Nix wrote: > > - /sbin/reboot -f of running system > -> Journal replay, no problems other than the expected free block > count problems. This is not such a severe problem after all! > > - Normal shutdown, but a 60 second pause after lazy umount, more than > long enough for all umounts to proceed to termination > -> no corruption, but curiously /home experienced a journal replay > before being fscked, even though a cat of /proc/mounts after > umounting revealed that the only mounted filesystem was /, > read-only, so /home should have been clean Question: how are you doing the journal replay? Is it happening as part of running e2fsck, or are you mounting the file system and letting kernel do the journal replay? Also, can you reproduce the problem with the nobarrier and journal_async_commit options *removed*? Yes, I know you have battery backup, but it would be interesting to see if the problem shows up in the default configuration with none of the more specialist options. (So it would probably be good to test with journal_checksum removed as well.) If that does make the problem go away, that will be a very interesting data point.... > Unfortunately, the massive corruption in the last testcase was seen in > 3.6.1 as well as 3.6.3: it appears that the only effect that superblock > change had in 3.6.3 was to make this problem easier to hit, and that the > bug itself was introduced probably somewhere between 3.5 and 3.6 (though > I only rebooted 3.5.x twice, and it's rare enough before 3.6.[23], at > ~1/20 boots, that it may have been present for longer and I never > noticed). Hmm.... ok. Can you tell whether or not the 2nd patch I posted on this thread made any difference to how frequently it happened? The main difference with 3.6.3 with 2nd patch applied compared to 3.6.1 is that if it detects that the journal superblock update is a no-op, it skips the write request. With 3.6.1, it submits the journal superblock write regardless of whether or not it would be a no-op. So if my patch isn't making a difference to the freqency to when you are seeing the corruption, then it must be the write request itself which is important. When you say it's rare before 3.6.[23], how rare is it? How reliably can you trigger it under 3.6.1? One in 3? One in 5? One in 20? As far as bisecting, one experiment that I'd really appreciate your doing is to check and see whether you can reproduce the problem using the 3.4 kernel, and if you can, to see if it reproduces under the 3.3 kernel. The reason why I ask this is there were not any major changes between 3.5 and 3.6, or between 3.4 and 3.5. There *were* however, some fairly major changes made by Jan Kara that were introduced between 3.3 and 3.4. Among other things, this is where we started using FUA (Force Unit Attention) writes to update the journal superblock instead of just using REQ_FLUSH. This is in fact the most likely place where we might have introduced the regression, since it wouldn't surprise me if Jan didn't test the case of using nobarrier with a storage array with battery backup (I certainly didn't, since I don't have easy access to such fancy toys :-). > It also appears impossible for me to reliably shut my system down, > though a 60s timeout after lazy umount and before reboot is likely to > work in all but the most pathological of cases (where a downed NFS > server comes up at just the wrong instant): it is clear that the > previous 5s timeout eventually became insufficient simply because of the > amount of time it can take to do a umount on today's larger filesystems. Something that you might want to consider trying is after you kill all of the processes, remount all of the local disk file systems read-only, then kick off the unmount of the NFS file systems (just to be nice to the NFS servers, so they are notified of the unmount), and then just force the reboot. If the file systems have been remounted r/o, that will cause the journal to be shutdown cleanly, and all of the write flushed out. (Modulo issues with nobarrier, but that's a separate issue. I'm now thinking that a smart thing to do might be force a flush on an unmount or remount r/o, regardless of whether nobarrier is specified, just to make sure everything is written out before the poweroff, battery backup or no.) Regards, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 25 Oct 2012, Theodore Ts'o stated: > On Thu, Oct 25, 2012 at 12:27:02AM +0100, Nix wrote: >> >> - /sbin/reboot -f of running system >> -> Journal replay, no problems other than the expected free block >> count problems. This is not such a severe problem after all! >> >> - Normal shutdown, but a 60 second pause after lazy umount, more than >> long enough for all umounts to proceed to termination >> -> no corruption, but curiously /home experienced a journal replay >> before being fscked, even though a cat of /proc/mounts after >> umounting revealed that the only mounted filesystem was /, >> read-only, so /home should have been clean > > Question: how are you doing the journal replay? Is it happening as > part of running e2fsck, or are you mounting the file system and > letting kernel do the journal replay? This most recent instance was e2fsck. Normally, it's mount. Both seem able to yield the same corruption. > Also, can you reproduce the problem with the nobarrier and > journal_async_commit options *removed*? Yes, I know you have battery > backup, but it would be interesting to see if the problem shows up in > the default configuration with none of the more specialist options. > (So it would probably be good to test with journal_checksum removed as > well.) I'll try that, hopefully tomorrow sometime. It's 2:30am now and probably time to sleep. >> Unfortunately, the massive corruption in the last testcase was seen in >> 3.6.1 as well as 3.6.3: it appears that the only effect that superblock >> change had in 3.6.3 was to make this problem easier to hit, and that the >> bug itself was introduced probably somewhere between 3.5 and 3.6 (though >> I only rebooted 3.5.x twice, and it's rare enough before 3.6.[23], at >> ~1/20 boots, that it may have been present for longer and I never >> noticed). > > Hmm.... ok. Can you tell whether or not the 2nd patch I posted on > this thread made any difference to how frequently it happened? The Well, I had a couple of reboots without corruption with that patch applied, and /home was only ever corrupted with it not applied -- but that could perfectly well be chance, since I only had two or three instances of /home corruption so far, thank goodness. > When you say it's rare before 3.6.[23], how rare is it? How reliably > can you trigger it under 3.6.1? One in 3? One in 5? One in 20? I've rebooted out of 3.6.1 about fifteen times so far. I've seen once instance of corruption. I've never seen it before 3.6, but I only rebooted 3.5.x or 3.4.x once or twice in total, so that too could be chance. > As far as bisecting, one experiment that I'd really appreciate your > doing is to check and see whether you can reproduce the problem using > the 3.4 kernel, and if you can, to see if it reproduces under the 3.3 > kernel. Will try. It might be the weekend before I can find the time though :( > The reason why I ask this is there were not any major changes between > 3.5 and 3.6, or between 3.4 and 3.5. There *were* however, some > fairly major changes made by Jan Kara that were introduced between 3.3 > and 3.4. Among other things, this is where we started using FUA > (Force Unit Attention) writes to update the journal superblock instead > of just using REQ_FLUSH. This is in fact the most likely place where > we might have introduced the regression, since it wouldn't surprise me > if Jan didn't test the case of using nobarrier with a storage array > with battery backup (I certainly didn't, since I don't have easy > access to such fancy toys :-). Hm. At boot, I see this for both volumes on the Areca controller: [ 0.855376] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA [ 0.855465] sd 0:0:0:1: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA So it looks to me like FUA changes themselves could have little effect. (btw, the controller cost only about £150... if it was particularly fancy I certainly couldn't have afforded it.) >> It also appears impossible for me to reliably shut my system down, >> though a 60s timeout after lazy umount and before reboot is likely to >> work in all but the most pathological of cases (where a downed NFS >> server comes up at just the wrong instant): it is clear that the >> previous 5s timeout eventually became insufficient simply because of the >> amount of time it can take to do a umount on today's larger filesystems. > > Something that you might want to consider trying is after you kill all > of the processes, remount all of the local disk file systems > read-only, then kick off the unmount of the NFS file systems (just to > be nice to the NFS servers, so they are notified of the unmount), and Actually I umount NFS first of all, because if I kill the processes first, this causes trouble with the NFS unmounts, particularly if I'm doing self-mounting (which I do sometimes, though not at the moment). I will certainly try a readonly remount instead. > force a flush on an unmount or remount r/o, regardless of whether > nobarrier is specified, just to make sure everything is written out > before the poweroff, battery backup or no.) I'm rather surprised that doesn't happen anyway. I always thought it did.
On 25 Oct 2012, Theodore Ts'o stated: > Also, can you reproduce the problem with the nobarrier and > journal_async_commit options *removed*? Yes, I know you have battery > backup, but it would be interesting to see if the problem shows up in > the default configuration with none of the more specialist options. > (So it would probably be good to test with journal_checksum removed as > well.) I'm going to spend some time after work today trying to reproduce this in a virtual machine. If rebooting while umounting is truly all it takes, as it seems, this should eliminate a bunch of variables and make it a lot easier to reproduce. (Assuming Eric hasn't already done just that, that is.)
I've been thinking about this some more, and if you don't have a lot of time, perhaps the most important test to do is this. Does the chance of your seeing corrupted files in v3.6.3 go down if you run 3.6.3 with commit 14b4ed22a6 reverted? Keep your current configuration, using nobarrier, et. al, constant. If reverting the commit makes things better, then that's what would be most useful to know as soon as possible, since the correct short-term solution is to revert that commit for 3.7-rcX, as well as the 3.6 and 3.5 stable kernels. We can investigate later whether nobarrier, journal_async_commit seem to make the problem worse, and whether the less common corruption case that you were seeing with 3.6.1 was actually a change which was introduced between 3.3 and 3.4. But most importantly, even if the bug doesn't show up with the default mount options at all (which explains why Eric and I weren't able to reproduce it), there are probably other users using nobarrier, so if the frequency with which you were seeing corruptions went up significantly between 3.6.1 and 3.6.3, and reverting 14b4ed22a6 brings the frequency back down to what you were seeing with 3.6.1, we should do that ASAP. Regards, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 25 Oct 2012, Theodore Ts'o stated: > I've been thinking about this some more, and if you don't have a lot > of time, I've got time, but it's this weekend, not during the week :) > perhaps the most important test to do is this. Does the > chance of your seeing corrupted files in v3.6.3 go down if you run > 3.6.3 with commit 14b4ed22a6 reverted? This I can verify, sometime this evening. (I presume what we're really interested in is whether the window in which files get corrupted has narrowed such that my 5s sleep after umount is now long enough to have a lower likelihood of corruption, since we know that a near-0s sleep after umount causes corruption almost every time on 3.6.1 as well: I've now done that three times and got corruption every time.) > But most importantly, even if the bug doesn't show up with the default > mount options at all (which explains why Eric and I weren't able to > reproduce it), there are probably other users using nobarrier, so if > the frequency with which you were seeing corruptions went up > significantly between 3.6.1 and 3.6.3, and reverting 14b4ed22a6 brings > the frequency back down to what you were seeing with 3.6.1, we should > do that ASAP. Agreed.
On 25 Oct 2012, nix@esperi.org.uk said:
> This I can verify, sometime this evening.
Sometime *tomorrow* evening. This has been quite stressful and I can
hardly keep my eyes open. I'm not doing anything risky in this state.
On 25 Oct 2012, Theodore Ts'o told this: > If that does make the problem go away, that will be a very interesting > data point.... I'll be looking at this tomorrow, but as sod's law would have it I have another user on this machine who didn't want it mega-rebooted tonight, so I was reduced to trying to reproduce the problem in virtualization under qemu. I failed, for one very simple reason: on 3.6.3, even with a umount -l still in the process of unmounting the fs and flushing changes, even on an fs mounted nobarrier,journal_async_commit, even when mounted atop LVM, reboot(2) will block until umount's writeout is complete (and lvm vgchange refuses to deactivate the volume group while that is happening, but I don't bother deactivating volume groups on the afflicted machine so I know that can't be related). Obviously, this suffices to ensure that a reboot is not possible while umounts are underway -- though a power cut is still possible, I suppose. On the afflicted machine (with a block device stack running LVM, then libata/arcmsr), as far as I can tell reboot(8) is *not* blocking if a unmount is underway: it shoots down everything and restarts at once. I have no direct proof of this yet, but during the last week I've routinely seen it reboot with lots of writes underway and umount -l log messages streaming up the screen: it certainly doesn't wait for all the umount -l's to be done the way it is in virtualization. I have no idea how this can be possible: I thought fses on a block device had to be quiesced (thus, in the case of an ongoing umount, unmounted and flushed) before any attempt at all was made to shut the underlying block device down, and I'd be fairly surprised if a flush wasn't done even if nobarrier was active (it certainly seems to be for virtio-blk, but that may well be a special case). But arcmsr (or libata? I should test with a simulated libata rather than virtio-blk next) appears to be getting around that somehow. This would probably explain all sorts of horrible corruption if umounting during a reboot, right? So maybe it's the stack of block devices that's at fault, and not the filesystem at all! I'll admit I don't really understand what happens at system halt time well enough to be sure, and getting log info from a machine in the middle of reboot(8) appears likely to be a complete sod (maybe halt(8) would be better: at least I could take a photo of the screen then). If that's true, it would *certainly* explain why nobody else can see this problem: only arcmsr users who also do umount -l's would have a chance, and that population probably has a size of one. I'll try to prove this tomorrow by writing a few gigs of junk to a temp filesytem held open by a temporary cat /dev/null, umount -l'ing it and killing off the cat the instant before the reboot -f call. If I don't see the reboot call blocking, the hypothesis is proved. (This is much what I did in virtualization, where I observe reboot blocking.) (Another blockdev-related possibility, if reboot *is* observed to block, is that arcmsr may be throwing away very-recently-written data when the adapter is shut down right before reboot.) Argh. How can rebooting a system be so damn complicated. Bring back the C64 or BBC Master where I could just pull the power lead out and stick it back in. :) -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
=============
22a5672 ext4: online defrag is not supported for journaled files
ba57d9e ext4: move_extent code cleanup
No behavioral change unless e4defrag has been used.
Online Resize
=============
5018ddd ext4: avoid duplicate writes of the backup bg descriptor blocks
256ae46 ext4: don't copy non-existent gdt blocks when resizing
416a688 ext4: ignore last group w/o enough space when resizing instead of BUG'ing
No observable change unless online resizing (e2resize) has been used
Other Commits
=============
92b7722 ext4: fix mtime update in nodelalloc mode
Changes where we call file_update_time()
34414b2 ext4: fix fdatasync() for files with only i_size changes
Forces the inode changes to be commited if only i_sync changes when
fdatasync() is called. No changes except performance impact
to fdatasync() and correctness after a system crash.
12ebdf0 ext4: always set i_op in ext4_mknod()
Fixes a bug if CONFIG_EXT4_FS_XATTR is not defined;
no change if CONFIG_EXT4_FS_XATTR is defined
2fdb112 ext4: fix crash when accessing /proc/mounts concurrently
Remove an erroneous "static" for an function so it is allocated on the stack;
fixes a bug if two processes cat /proc/mounts at the same time
1638f1f ext4: fix potential deadlock in ext4_nonda_switch()
Fixes a circular lock dependency
14b4ed2 jbd2: don't write superblock when if its empty
If journal->s_start is zero, we may not update journal->s_sequence when
it might be needed. (But we at the moement we can't see how this could
lead to the reported fs corruptions.)
commit cb57108637e01ec2f02d9311cedc3013e96f25d4
Author: Theodore Ts'o <tytso@mit.edu>
Date: Wed Oct 24 01:01:41 2012 -0400
jbd2: fix a potential fs corrupting bug in jbd2_mark_journal_empty
Fix a potential file system corrupting bug which was introduced by
commit eeecef0af5ea4efd763c9554cf2bd80fc4a0efd3: jbd2: don't write
superblock when if its empty.
We should only skip writing the journal superblock if there is nothing
to do --- not just when s_start is zero.
This has caused users to report file system corruptions in ext4 that
look like this:
EXT4-fs error (device sdb3): ext4_mb_generate_buddy:741: group 436, 22902 clusters in bitmap, 22901 in gd
JBD2: Spotted dirty metadata buffer (dev = sdb3, blocknr = 0). There's a risk of filesystem corruption in case of system crash.
after the file system has been corrupted.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 0f16edd..26b2983 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1351,24 +1351,33 @@ void jbd2_journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
static void jbd2_mark_journal_empty(journal_t *journal)
{
journal_superblock_t *sb = journal->j_superblock;
+ __be32 new_tail_sequence;
BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
read_lock(&journal->j_state_lock);
- /* Is it already empty? */
+ new_tail_sequence = cpu_to_be32(journal->j_tail_sequence);
+ /* Nothing to do? */
if (sb->s_start == 0) {
+ pr_err("JBD2: jbd2_mark_journal_empty bug workaround (%u, %u)\n",
+ (unsigned) be32_to_cpu(sb->s_sequence),
+ (unsigned) be32_to_cpu(new_tail_sequence));
+ WARN_ON(1);
+ }
+ if (sb->s_start == 0 && sb->s_sequence == new_tail_sequence) {
read_unlock(&journal->j_state_lock);
- return;
+ goto set_flushed;
}
jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
journal->j_tail_sequence);
- sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
+ sb->s_sequence = new_tail_sequence;
sb->s_start = cpu_to_be32(0);
read_unlock(&journal->j_state_lock);
jbd2_write_superblock(journal, WRITE_FUA);
- /* Log is no longer empty */
+set_flushed:
+ /* Log is empty */
write_lock(&journal->j_state_lock);
journal->j_flags |= JBD2_FLUSHED;
write_unlock(&journal->j_state_lock);