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();
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
fs/dcache.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 98cc4508e140..0d0ba5b2a8ae 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1035,8 +1035,10 @@ ascend:
write_sequnlock(&rename_lock);
return 0; /* No mount points found in tree */
positive:
- if (!locked && read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq)) {
+ rcu_read_lock();
goto rename_retry;
+ }
if (locked)
write_sequnlock(&rename_lock);
return 1;
--
2.1.4
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