Messages in this thread Patch in this message | | | From | OGAWA Hirofumi <> | Subject | Re: [2.6.29-rc5][BUG] swapon on vfat file gets stuck on inode lock | Date | Thu, 12 Mar 2009 02:03:23 +0900 |
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Linus Torvalds <torvalds@linux-foundation.org> writes:
> Yes, clearly there's a deadlock there which was hidden before. And FAT > technically does the locking right, so that bmap() doesn't race with > somebody changing the file. > > That said, other filesystems don't have this problem, simply because they > just ignore the race, knowing that bmap is inherently racy in that > situation _anyway_ (ie the value we return is clearly going to race > _after_ we release the lock even if we do the lookup with the lock held!). > > So the right thing to do would appear to be to just remove the silly > locking in fat_bmap. It's not helping, and it's clearly hurting your > (crazy) case. In the _normal_ paths (ie a regular read/write) we handle > locking on a per-page basis anyway. > > I dunno. No other filesystem has _any_ locking in their bmap that I can > see, so I strongly suspect that fat doesn't need it either. > > IOW, I'm almost 100% sure that the right fix is this trivial one, but I'd > like somebody else to double-check my thinking.
I'm sure that path touch the metadata without locking (so, reused entry can not be for that inode anymore). However, I guess the result doesn't become any fs corruption, so and other fs is ignoring the possibly wrong result of bmap().
I'm thinking to use this patch instead of removing.
[PATCH] Fix _fat_bmap() locking
On swapon() path, it has already i_mutex. So, this uses i_alloc_sem instead of it.
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> ---
fs/fat/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN fs/fat/inode.c~fat_bmap-locking-fix fs/fat/inode.c --- linux-2.6/fs/fat/inode.c~fat_bmap-locking-fix 2009-03-12 00:47:15.000000000 +0900 +++ linux-2.6-hirofumi/fs/fat/inode.c 2009-03-12 00:47:42.000000000 +0900 @@ -202,9 +202,9 @@ static sector_t _fat_bmap(struct address sector_t blocknr; /* fat_get_cluster() assumes the requested blocknr isn't truncated. */ - mutex_lock(&mapping->host->i_mutex); + down_read(&mapping->host->i_alloc_sem); blocknr = generic_block_bmap(mapping, block, fat_get_block); - mutex_unlock(&mapping->host->i_mutex); + up_read(&mapping->host->i_alloc_sem); return blocknr; } _ -- OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
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