| Message ID | 20120529200856.GF23991@quack.suse.cz |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Tue, May 29, 2012 at 10:08:56PM +0200, Jan Kara wrote: > On Tue 29-05-12 21:50:19, Jan Kara wrote: > > On Mon 28-05-12 17:05:11, Ted Tso wrote: > > > On Mon, May 28, 2012 at 02:29:05PM -0600, Andreas Dilger wrote: > > > > This patch is good from the POV of covering all filesystems, and > > > > avoiding the deadlock at the dcache level. It would be possible to > > > > detect this problem in the filesystem itself during lookup, before > > > > the bad link got into the dcache itself. Something like: > > > > > > I like that as a solution for detecting the problem in ext4. As you > > > say, it's still an issue for other file systems, and so the patch I > > > proposed is still probably a good idea for the VFS. But this way ext4 > > > (and ext3 when Jan backports it) will be able to detect the problem > > > and mark the file system as being corrupted. > > Actually, I think there's even better way. d_splice_alias() can rather > > easily detect the problem and report it to filesystem. The advantage is > > that the check in d_splice_alias() can catch any "hardlinks" to > > directories, not just self loops. The patch is attached, I also have > > corresponding handling written for ext? filesystems but that's trivial. > > I'll post the whole series to Al to have a look. > And now with the attachment. Sorry. Well, my understanding of d_splice_alias is that it should just return the existing dentry instead of failing. (It does that now for DISCONNECTED dentries, but I don't understand why they're special.) So that's what: http://git.kernel.org/?p=linux/kernel/git/viro/vfs.git;a=commit;h=9d345b3217b384813680901d42eae3fb380b9f77 does. --b. > > Honza > >From 0715b656ac88ce1bb62800b14d99ef2e25c26d28 Mon Sep 17 00:00:00 2001 > From: Jan Kara <jack@suse.cz> > Date: Tue, 29 May 2012 21:19:01 +0200 > Subject: [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems > > When a directory hierarchy is corrupted (e. g. due to a bit flip on the media), > it can happen that it contains loops of directories. That creates possibilities > for deadlock when locking directories. > > Fix the problem by checking in d_splice_alias() that when we splice a > directory, it does not have any other connected alias. > > Reported-by: Sami Liedes <sami.liedes@iki.fi> > Signed-off-by: Jan Kara <jack@suse.cz> > --- > fs/dcache.c | 4 ++++ > 1 files changed, 4 insertions(+), 0 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index 4435d8b..ca31a1e 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -1658,6 +1658,10 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) > d_move(new, dentry); > iput(inode); > } else { > + if (unlikely(!list_empty(&inode->i_dentry))) { > + spin_unlock(&inode->i_lock); > + return ERR_PTR(-EIO); > + } > /* already taking inode->i_lock, so d_add() by hand */ > __d_instantiate(dentry, inode); > spin_unlock(&inode->i_lock); > -- > 1.7.1 > -- 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 Wed 30-05-12 13:37:09, J. Bruce Fields wrote: > On Tue, May 29, 2012 at 10:08:56PM +0200, Jan Kara wrote: > > On Tue 29-05-12 21:50:19, Jan Kara wrote: > > > On Mon 28-05-12 17:05:11, Ted Tso wrote: > > > > On Mon, May 28, 2012 at 02:29:05PM -0600, Andreas Dilger wrote: > > > > > This patch is good from the POV of covering all filesystems, and > > > > > avoiding the deadlock at the dcache level. It would be possible to > > > > > detect this problem in the filesystem itself during lookup, before > > > > > the bad link got into the dcache itself. Something like: > > > > > > > > I like that as a solution for detecting the problem in ext4. As you > > > > say, it's still an issue for other file systems, and so the patch I > > > > proposed is still probably a good idea for the VFS. But this way ext4 > > > > (and ext3 when Jan backports it) will be able to detect the problem > > > > and mark the file system as being corrupted. > > > Actually, I think there's even better way. d_splice_alias() can rather > > > easily detect the problem and report it to filesystem. The advantage is > > > that the check in d_splice_alias() can catch any "hardlinks" to > > > directories, not just self loops. The patch is attached, I also have > > > corresponding handling written for ext? filesystems but that's trivial. > > > I'll post the whole series to Al to have a look. > > And now with the attachment. Sorry. > > Well, my understanding of d_splice_alias is that it should just return > the existing dentry instead of failing. (It does that now for > DISCONNECTED dentries, but I don't understand why they're special.) > So that's what: > > http://git.kernel.org/?p=linux/kernel/git/viro/vfs.git;a=commit;h=9d345b3217b384813680901d42eae3fb380b9f77 > > does. Thanks for the pointer. In the case I tried to solve, returning the existing dentry will solve the deadlocks, just user won't be warned that the filesystem is corrupted. Since you seem to describe a valid case where we can spot other !DISCONNECTED dentry of a directory, I guess we have no other choice than using your approach. We could do some sanity checks in ->lookup method (like Andreas suggested) but they are not that powerful as a check in d_splice_alias() can be. But what can one do... Honza > > >From 0715b656ac88ce1bb62800b14d99ef2e25c26d28 Mon Sep 17 00:00:00 2001 > > From: Jan Kara <jack@suse.cz> > > Date: Tue, 29 May 2012 21:19:01 +0200 > > Subject: [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems > > > > When a directory hierarchy is corrupted (e. g. due to a bit flip on the media), > > it can happen that it contains loops of directories. That creates possibilities > > for deadlock when locking directories. > > > > Fix the problem by checking in d_splice_alias() that when we splice a > > directory, it does not have any other connected alias. > > > > Reported-by: Sami Liedes <sami.liedes@iki.fi> > > Signed-off-by: Jan Kara <jack@suse.cz> > > --- > > fs/dcache.c | 4 ++++ > > 1 files changed, 4 insertions(+), 0 deletions(-) > > > > diff --git a/fs/dcache.c b/fs/dcache.c > > index 4435d8b..ca31a1e 100644 > > --- a/fs/dcache.c > > +++ b/fs/dcache.c > > @@ -1658,6 +1658,10 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) > > d_move(new, dentry); > > iput(inode); > > } else { > > + if (unlikely(!list_empty(&inode->i_dentry))) { > > + spin_unlock(&inode->i_lock); > > + return ERR_PTR(-EIO); > > + } > > /* already taking inode->i_lock, so d_add() by hand */ > > __d_instantiate(dentry, inode); > > spin_unlock(&inode->i_lock); > > -- > > 1.7.1 > > >
On Wed, May 30, 2012 at 10:12:57PM +0200, Jan Kara wrote: > On Wed 30-05-12 13:37:09, J. Bruce Fields wrote: > > On Tue, May 29, 2012 at 10:08:56PM +0200, Jan Kara wrote: > > > On Tue 29-05-12 21:50:19, Jan Kara wrote: > > > > On Mon 28-05-12 17:05:11, Ted Tso wrote: > > > > > On Mon, May 28, 2012 at 02:29:05PM -0600, Andreas Dilger wrote: > > > > > > This patch is good from the POV of covering all filesystems, and > > > > > > avoiding the deadlock at the dcache level. It would be possible to > > > > > > detect this problem in the filesystem itself during lookup, before > > > > > > the bad link got into the dcache itself. Something like: > > > > > > > > > > I like that as a solution for detecting the problem in ext4. As you > > > > > say, it's still an issue for other file systems, and so the patch I > > > > > proposed is still probably a good idea for the VFS. But this way ext4 > > > > > (and ext3 when Jan backports it) will be able to detect the problem > > > > > and mark the file system as being corrupted. > > > > Actually, I think there's even better way. d_splice_alias() can rather > > > > easily detect the problem and report it to filesystem. The advantage is > > > > that the check in d_splice_alias() can catch any "hardlinks" to > > > > directories, not just self loops. The patch is attached, I also have > > > > corresponding handling written for ext? filesystems but that's trivial. > > > > I'll post the whole series to Al to have a look. > > > And now with the attachment. Sorry. > > > > Well, my understanding of d_splice_alias is that it should just return > > the existing dentry instead of failing. (It does that now for > > DISCONNECTED dentries, but I don't understand why they're special.) > > So that's what: > > > > http://git.kernel.org/?p=linux/kernel/git/viro/vfs.git;a=commit;h=9d345b3217b384813680901d42eae3fb380b9f77 > > > > does. > Thanks for the pointer. In the case I tried to solve, returning the > existing dentry will solve the deadlocks, just user won't be warned that > the filesystem is corrupted. Since you seem to describe a valid case where > we can spot other !DISCONNECTED dentry of a directory, I guess we have no > other choice than using your approach. But my patch got reverted, on suspicion that it was either wrong or covering up some other problem: http://marc.info/?l=linux-fsdevel&m=133917767003505&w=2 ... which an approach like yours might help at least find? So maybe it's worth another try. --b. > > We could do some sanity checks in ->lookup method (like Andreas suggested) > but they are not that powerful as a check in d_splice_alias() can be. But > what can one do... > > Honza > > > > > >From 0715b656ac88ce1bb62800b14d99ef2e25c26d28 Mon Sep 17 00:00:00 2001 > > > From: Jan Kara <jack@suse.cz> > > > Date: Tue, 29 May 2012 21:19:01 +0200 > > > Subject: [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems > > > > > > When a directory hierarchy is corrupted (e. g. due to a bit flip on the media), > > > it can happen that it contains loops of directories. That creates possibilities > > > for deadlock when locking directories. > > > > > > Fix the problem by checking in d_splice_alias() that when we splice a > > > directory, it does not have any other connected alias. > > > > > > Reported-by: Sami Liedes <sami.liedes@iki.fi> > > > Signed-off-by: Jan Kara <jack@suse.cz> > > > --- > > > fs/dcache.c | 4 ++++ > > > 1 files changed, 4 insertions(+), 0 deletions(-) > > > > > > diff --git a/fs/dcache.c b/fs/dcache.c > > > index 4435d8b..ca31a1e 100644 > > > --- a/fs/dcache.c > > > +++ b/fs/dcache.c > > > @@ -1658,6 +1658,10 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) > > > d_move(new, dentry); > > > iput(inode); > > > } else { > > > + if (unlikely(!list_empty(&inode->i_dentry))) { > > > + spin_unlock(&inode->i_lock); > > > + return ERR_PTR(-EIO); > > > + } > > > /* already taking inode->i_lock, so d_add() by hand */ > > > __d_instantiate(dentry, inode); > > > spin_unlock(&inode->i_lock); > > > -- > > > 1.7.1 > > > > > > -- > Jan Kara <jack@suse.cz> > SUSE Labs, CR > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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 Mon 18-06-12 17:19:30, J. Bruce Fields wrote: > On Wed, May 30, 2012 at 10:12:57PM +0200, Jan Kara wrote: > > On Wed 30-05-12 13:37:09, J. Bruce Fields wrote: > > > On Tue, May 29, 2012 at 10:08:56PM +0200, Jan Kara wrote: > > > > On Tue 29-05-12 21:50:19, Jan Kara wrote: > > > > > On Mon 28-05-12 17:05:11, Ted Tso wrote: > > > > > > On Mon, May 28, 2012 at 02:29:05PM -0600, Andreas Dilger wrote: > > > > > > > This patch is good from the POV of covering all filesystems, and > > > > > > > avoiding the deadlock at the dcache level. It would be possible to > > > > > > > detect this problem in the filesystem itself during lookup, before > > > > > > > the bad link got into the dcache itself. Something like: > > > > > > > > > > > > I like that as a solution for detecting the problem in ext4. As you > > > > > > say, it's still an issue for other file systems, and so the patch I > > > > > > proposed is still probably a good idea for the VFS. But this way ext4 > > > > > > (and ext3 when Jan backports it) will be able to detect the problem > > > > > > and mark the file system as being corrupted. > > > > > Actually, I think there's even better way. d_splice_alias() can rather > > > > > easily detect the problem and report it to filesystem. The advantage is > > > > > that the check in d_splice_alias() can catch any "hardlinks" to > > > > > directories, not just self loops. The patch is attached, I also have > > > > > corresponding handling written for ext? filesystems but that's trivial. > > > > > I'll post the whole series to Al to have a look. > > > > And now with the attachment. Sorry. > > > > > > Well, my understanding of d_splice_alias is that it should just return > > > the existing dentry instead of failing. (It does that now for > > > DISCONNECTED dentries, but I don't understand why they're special.) > > > So that's what: > > > > > > http://git.kernel.org/?p=linux/kernel/git/viro/vfs.git;a=commit;h=9d345b3217b384813680901d42eae3fb380b9f77 > > > > > > does. > > Thanks for the pointer. In the case I tried to solve, returning the > > existing dentry will solve the deadlocks, just user won't be warned that > > the filesystem is corrupted. Since you seem to describe a valid case where > > we can spot other !DISCONNECTED dentry of a directory, I guess we have no > > other choice than using your approach. > > But my patch got reverted, on suspicion that it was either wrong or > covering up some other problem: > > http://marc.info/?l=linux-fsdevel&m=133917767003505&w=2 > > ... which an approach like yours might help at least find? So maybe > it's worth another try. Yeah, I'll rebase and resubmit those patches (plus fixup error handling as Al suggested) today or tomorrow. Honza
From 0715b656ac88ce1bb62800b14d99ef2e25c26d28 Mon Sep 17 00:00:00 2001 From: Jan Kara <jack@suse.cz> Date: Tue, 29 May 2012 21:19:01 +0200 Subject: [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems When a directory hierarchy is corrupted (e. g. due to a bit flip on the media), it can happen that it contains loops of directories. That creates possibilities for deadlock when locking directories. Fix the problem by checking in d_splice_alias() that when we splice a directory, it does not have any other connected alias. Reported-by: Sami Liedes <sami.liedes@iki.fi> Signed-off-by: Jan Kara <jack@suse.cz> --- fs/dcache.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 4435d8b..ca31a1e 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1658,6 +1658,10 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) d_move(new, dentry); iput(inode); } else { + if (unlikely(!list_empty(&inode->i_dentry))) { + spin_unlock(&inode->i_lock); + return ERR_PTR(-EIO); + } /* already taking inode->i_lock, so d_add() by hand */ __d_instantiate(dentry, inode); spin_unlock(&inode->i_lock); -- 1.7.1