| From | Andi Kleen <> | Subject | [PATCH] [77/275] dm: dont take i_mutex to change device size | Date | Wed, 30 Mar 2011 14:05:14 -0700 (PDT) |
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2.6.35-longterm review patch. If anyone has any objections, please let me know.
------------------ From: Mike Snitzer <snitzer@redhat.com>
commit c217649bf2d60ac119afd71d938278cffd55962b upstream.
No longer needlessly hold md->bdev->bd_inode->i_mutex when changing the size of a DM device. This additional locking is unnecessary because i_size_write() is already protected by the existing critical section in dm_swap_table(). DM already has a reference on md->bdev so the associated bd_inode may be changed without lifetime concerns.
A negative side-effect of having held md->bdev->bd_inode->i_mutex was that a concurrent DM device resize and flush (via fsync) would deadlock. Dropping md->bdev->bd_inode->i_mutex eliminates this potential for deadlock. The following reproducer no longer deadlocks: https://www.redhat.com/archives/dm-devel/2009-July/msg00284.html
Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Andi Kleen <ak@linux.intel.com>
--- drivers/md/dm.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
Index: linux-2.6.35.y/drivers/md/dm.c =================================================================== --- linux-2.6.35.y.orig/drivers/md/dm.c 2011-03-29 22:51:39.284717971 -0700 +++ linux-2.6.35.y/drivers/md/dm.c 2011-03-29 23:02:59.762306252 -0700 @@ -2040,13 +2040,14 @@ wake_up(&md->eventq); } +/* + * Protected by md->suspend_lock obtained by dm_swap_table(). + */ static void __set_size(struct mapped_device *md, sector_t size) { set_capacity(md->disk, size); - mutex_lock(&md->bdev->bd_inode->i_mutex); i_size_write(md->bdev->bd_inode, (loff_t)size << SECTOR_SHIFT); - mutex_unlock(&md->bdev->bd_inode->i_mutex); } /*
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