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authorBen Hutchings <ben@decadent.org.uk>2015-02-11 03:16:35 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-04-29 10:34:02 +0200
commitc190d250d8db5620218d5d56999580ed8488ec24 (patch)
tree5daab86e88a5c12592cd6de54cace98272d3ff99
parent9e505ae71ac8c8f643498a9e8c01ace136140606 (diff)
dcache: Fix locking bugs in backported "deal with deadlock in d_walk()"
commit 20defcec264ceab2630356fb9d397f3d237b5e6d upstream in 3.2-stable Steven Rostedt reported: > Porting -rt to the latest 3.2 stable tree I triggered this bug: > > ===================================== > [ BUG: bad unlock balance detected! ] > ------------------------------------- > rm/1638 is trying to release lock (rcu_read_lock) at: > [<c04fde6c>] rcu_read_unlock+0x0/0x23 > but there are no more locks to release! > > other info that might help us debug this: > 2 locks held by rm/1638: > #0: (&sb->s_type->i_mutex_key#9/1){+.+.+.}, at: [<c04f93eb>] do_rmdir+0x5f/0xd2 > #1: (&sb->s_type->i_mutex_key#9){+.+.+.}, at: [<c04f9329>] vfs_rmdir+0x49/0xac > > stack backtrace: > Pid: 1638, comm: rm Not tainted 3.2.66-test-rt96+ #2 > Call Trace: > [<c083f390>] ? printk+0x1d/0x1f > [<c0463cdf>] print_unlock_inbalance_bug+0xc3/0xcd > [<c04653a8>] lock_release_non_nested+0x98/0x1ec > [<c046228d>] ? trace_hardirqs_off_caller+0x18/0x90 > [<c0456f1c>] ? local_clock+0x2d/0x50 > [<c04fde6c>] ? d_hash+0x2f/0x2f > [<c04fde6c>] ? d_hash+0x2f/0x2f > [<c046568e>] lock_release+0x192/0x1ad > [<c04fde83>] rcu_read_unlock+0x17/0x23 > [<c04ff344>] shrink_dcache_parent+0x227/0x270 > [<c04f9348>] vfs_rmdir+0x68/0xac > [<c04f9424>] do_rmdir+0x98/0xd2 > [<c04f03ad>] ? fput+0x1a3/0x1ab > [<c084dd42>] ? sysenter_exit+0xf/0x1a > [<c0465b58>] ? trace_hardirqs_on_caller+0x118/0x149 > [<c04fa3e0>] sys_unlinkat+0x2b/0x35 > [<c084dd13>] sysenter_do_call+0x12/0x12 > > > > > There's a path to calling rcu_read_unlock() without calling > rcu_read_lock() in have_submounts(). > > goto positive; > > positive: > if (!locked && read_seqretry(&rename_lock, seq)) > goto rename_retry; > > rename_retry: > rcu_read_unlock(); > > in the above path, rcu_read_lock() is never done before calling > rcu_read_unlock(); I reviewed locking contexts in all three functions that I changed when backporting "deal with deadlock in d_walk()". It's actually worse than this: - We don't hold this_parent->d_lock at the 'positive' label in have_submounts(), but it is unlocked after 'rename_retry'. - There is an rcu_read_unlock() after the 'out' label in select_parent(), but it's not held at the 'goto out'. Fix all three lock imbalances. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Tested-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/dcache.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index b1b8a7e9db0c..efa4602e064f 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1072,7 +1072,7 @@ ascend:
return 0; /* No mount points found in tree */
positive:
if (!locked && read_seqretry(&rename_lock, seq))
- goto rename_retry;
+ goto rename_retry_unlocked;
if (locked)
write_sequnlock(&rename_lock);
return 1;
@@ -1082,6 +1082,7 @@ rename_retry:
rcu_read_unlock();
if (locked)
goto again;
+rename_retry_unlocked:
locked = 1;
write_seqlock(&rename_lock);
goto again;
@@ -1146,6 +1147,7 @@ resume:
*/
if (found && need_resched()) {
spin_unlock(&dentry->d_lock);
+ rcu_read_lock();
goto out;
}