From 193be0ee17dd7ea309ddab1093da17e5924d7f36 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 17 Sep 2009 05:31:37 +0200 Subject: [PATCH] kill-the-bkl/reiserfs: Fix induced mm->mmap_sem to sysfs_mutex dependency Alexander Beregalov reported the following warning: ======================================================= [ INFO: possible circular locking dependency detected ] 2.6.31-03149-gdcc030a #1 ------------------------------------------------------- udevadm/716 is trying to acquire lock: (&mm->mmap_sem){++++++}, at: [] might_fault+0x4a/0xa0 but task is already holding lock: (sysfs_mutex){+.+.+.}, at: [] sysfs_readdir+0x5a/0x200 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (sysfs_mutex){+.+.+.}: [...] -> #2 (&bdev->bd_mutex){+.+.+.}: [...] -> #1 (&REISERFS_SB(s)->lock){+.+.+.}: [...] -> #0 (&mm->mmap_sem){++++++}: [...] On reiserfs mount path, we take the reiserfs lock and while initializing the journal, we open the device, taking the bdev->bd_mutex. Then rescan_partition() may signal the change to sysfs. We have then the following dependency: reiserfs_lock -> bd_mutex -> sysfs_mutex Later, while entering reiserfs_readpage() after a pagefault in an mmaped reiserfs file, we are holding the mm->mmap_sem, and we are going to take the reiserfs lock too. We have then the following dependency: mm->mmap_sem -> reiserfs_lock which, expanded with the previous dependency gives us: mm->mmap_sem -> reiserfs_lock -> bd_mutex -> sysfs_mutex Now while entering the sysfs readdir path, we are holding the sysfs_mutex. And when we copy a directory entry to the user buffer, we might fault and then take the mm->mmap_sem lock. Which leads to the circular locking dependency reported. We can fix that by relaxing the reiserfs lock during the call to journal_init_dev(), which is the place where we open the mounted device. This is fine to relax the lock here because we are in the begining of the reiserfs mount path and there is nothing to protect at this time, the journal is not intialized. We just keep this lock around for paranoid reasons. Reported-by: Alexander Beregalov Tested-by: Alexander Beregalov Signed-off-by: Frederic Weisbecker Cc: Jeff Mahoney Cc: Chris Mason Cc: Ingo Molnar Cc: Alexander Beregalov Cc: Laurent Riffard --- fs/reiserfs/journal.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c index d23d6d7a45a6..04e3c42a085f 100644 --- a/fs/reiserfs/journal.c +++ b/fs/reiserfs/journal.c @@ -2801,11 +2801,27 @@ int journal_init(struct super_block *sb, const char *j_dev_name, goto free_and_return; } + /* + * We need to unlock here to avoid creating the following + * dependency: + * reiserfs_lock -> sysfs_mutex + * Because the reiserfs mmap path creates the following dependency: + * mm->mmap -> reiserfs_lock, hence we have + * mm->mmap -> reiserfs_lock ->sysfs_mutex + * This would ends up in a circular dependency with sysfs readdir path + * which does sysfs_mutex -> mm->mmap_sem + * This is fine because the reiserfs lock is useless in mount path, + * at least until we call journal_begin. We keep it for paranoid + * reasons. + */ + reiserfs_write_unlock(sb); if (journal_init_dev(sb, journal, j_dev_name) != 0) { + reiserfs_write_lock(sb); reiserfs_warning(sb, "sh-462", "unable to initialize jornal device"); goto free_and_return; } + reiserfs_write_lock(sb); rs = SB_DISK_SUPER_BLOCK(sb); -- GitLab