| Message ID | 1305268616-5167-1-git-send-email-lczerner@redhat.com |
|---|---|
| State | New, archived |
| Headers | show |
2011/05/13 15:36, Lukas Czerner wrote: > That is because due to defensive programming we planted a lot of > BUG_ON's to prevent the length of the gap cache to be zero, but in this > case it actually will be zero, because there will be no gap at the end > of the file. Um, I think there is a block (blocksize -1 byte) in gap. And this gap should be used for the next block searching. According to ext4_ext_in_cache(), len=0 means the special case which we have no cache extent, so len=0 should be disallowed. Moreover, if we create the file which has 2^32-1 offset, we can't get extent which starts from this offset with FIEMAP ioctl. That's why I think the maximum file size should be 2^32-1 * blocksize. Regards, Kazuya Mio -- 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
Hi Lukas, How do you think about my comment? Regards, Kazuya Mio 2011/05/13 17:55, Kazuya Mio wrote: > 2011/05/13 15:36, Lukas Czerner wrote: >> That is because due to defensive programming we planted a lot of >> BUG_ON's to prevent the length of the gap cache to be zero, but in this >> case it actually will be zero, because there will be no gap at the end >> of the file. > > Um, I think there is a block (blocksize -1 byte) in gap. > And this gap should be used for the next block searching. > According to ext4_ext_in_cache(), len=0 means the special case > which we have no cache extent, so len=0 should be disallowed. > > Moreover, if we create the file which has 2^32-1 offset, > we can't get extent which starts from this offset with FIEMAP ioctl. > That's why I think the maximum file size should be 2^32-1 * blocksize. > > Regards, > Kazuya Mio -- 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
Hi Kazuya, I am really sorry for late answer. I think you're partly right. my solution is not good, but I still think that your is not good as well. I need to look at this again and more closely, sorry. What do you think about this: ext4_ext_next_allocated_block() should return next allocated block, however instead it in some cases returns EXT_MAX_BLOCK, which points at the last logical block in a file, which however in some cases might be equal to the last not allocated block, not first allocated block in subsequent extent. And boom, we have (next == lblock). So if we want to really return next allocated block (or more specifically, next block which we can not allocate), we should in those cases return EXT_MAX_BLOCK+1. And we should do this in ext4_ext_put_gap_in_cache() as well when there is no extent yet. Also note that as I said EXT_MAX_BLOCK means maximum logical block, however we use it as lenght in ext4_ext_put_gap_in_cache() which does not sound right either. It seems all a little bit messy :-/. I need to look at it and try it to see if it would work, but I think it does make sense. What do you think? Thanks! -Lukas On Tue, 24 May 2011, Kazuya Mio wrote: > Hi Lukas, > How do you think about my comment? > > Regards, > Kazuya Mio > > 2011/05/13 17:55, Kazuya Mio wrote: > > 2011/05/13 15:36, Lukas Czerner wrote: > >> That is because due to defensive programming we planted a lot of > >> BUG_ON's to prevent the length of the gap cache to be zero, but in this > >> case it actually will be zero, because there will be no gap at the end > >> of the file. > > > > Um, I think there is a block (blocksize -1 byte) in gap. > > And this gap should be used for the next block searching. > > According to ext4_ext_in_cache(), len=0 means the special case > > which we have no cache extent, so len=0 should be disallowed. > > > > Moreover, if we create the file which has 2^32-1 offset, > > we can't get extent which starts from this offset with FIEMAP ioctl. > > That's why I think the maximum file size should be 2^32-1 * blocksize. > > > > Regards, > > Kazuya Mio >
2011/05/24 17:57, Lukas Czerner wrote: > Hi Kazuya, > > I am really sorry for late answer. I think you're partly right. my > solution is not good, but I still think that your is not good as well. I > need to look at this again and more closely, sorry. > > What do you think about this: ext4_ext_next_allocated_block() should > return next allocated block, however instead it in some cases returns > EXT_MAX_BLOCK, which points at the last logical block in a file, which > however in some cases might be equal to the last not allocated block, > not first allocated block in subsequent extent. And boom, we have (next > == lblock). I think so, too. > So if we want to really return next allocated block (or more > specifically, next block which we can not allocate), we should in those > cases return EXT_MAX_BLOCK+1. And we should do this in > ext4_ext_put_gap_in_cache() as well when there is no extent yet. Also > note that as I said EXT_MAX_BLOCK means maximum logical block, however > we use it as lenght in ext4_ext_put_gap_in_cache() which does not sound > right either. It seems all a little bit messy :-/. I need to look at it > and try it to see if it would work, but I think it does make sense. > > What do you think? AFAIK, it's the best way to fix this problem. But I have no idea that doesn't increase the size of struct ext4_ext_cache. I'm looking forward to seeing the patch. Regards, Kazuya Mio -- 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
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 4890d6f..779ca49 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -1944,7 +1944,6 @@ ext4_ext_put_in_cache(struct inode *inode, ext4_lblk_t block, __u32 len, ext4_fsblk_t start) { struct ext4_ext_cache *cex; - BUG_ON(len == 0); spin_lock(&EXT4_I(inode)->i_block_reservation_lock); cex = &EXT4_I(inode)->i_cached_extent; cex->ec_block = block; @@ -1991,7 +1990,7 @@ ext4_ext_put_gap_in_cache(struct inode *inode, struct ext4_ext_path *path, le32_to_cpu(ex->ee_block), ext4_ext_get_actual_len(ex), block); - BUG_ON(next == lblock); + BUG_ON((next == lblock) && (next != EXT_MAX_BLOCK)); len = next - lblock; } else { lblock = len = 0;
Kazuya Mio reported that he was able to hit BUG_ON(next == lblock) in ext4_ext_put_gap_in_cache() while creating a sparse file in extent format and fill the tail of file up to its end. We will hit the BUG_ON when we write the last block (2^32-1) into the sparse file. That is because due to defensive programming we planted a lot of BUG_ON's to prevent the length of the gap cache to be zero, but in this case it actually will be zero, because there will be no gap at the end of the file. We could fix that as Kazuya Mio suggested by lowering the max file size of extent format file by one block. But I do not think this is necessary and we should rather fix the BUG_ON's to allow invalidating the gap cache by setting its lenght to zero and this is what this commit is doing. The bug which this commit fixes can be reproduced as follows: dd if=/dev/zero of=/mnt/mp1/file bs=<blocksize> count=1 seek=$((2**32-2)) sync dd if=/dev/zero of=/mnt/mp1/file bs=<blocksize> count=1 seek=$((2**32-1)) Reported-by: Kazuya Mio <k-mio@sx.jp.nec.com> Signed-off-by: Lukas Czerner <lczerner@redhat.com> --- fs/ext4/extents.c | 3 +-- 1 files changed, 1 insertions(+), 2 deletions(-)