dm: dont take i_mutex to change device size
authorMike Snitzer <snitzer@redhat.com>
Thu, 13 Jan 2011 19:53:46 +0000 (19:53 +0000)
committerAlasdair G Kergon <agk@redhat.com>
Thu, 13 Jan 2011 19:53:46 +0000 (19:53 +0000)
commitc217649bf2d60ac119afd71d938278cffd55962b
tree5addf2130d59f9fab614d852ac8fe7724ef78c9f
parent581548db3b3c0f6e25b500329eb02e3c72e7acbe
dm: dont take i_mutex to change device size

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>
Cc: stable@kernel.org
drivers/md/dm.c