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authorRobert Richter <robert.richter@amd.com>2011-05-31 12:35:41 +0200
committerRobert Richter <robert.richter@amd.com>2011-05-31 16:33:35 +0200
commitfe47ae7f53e179d2ef6771024feb000cbb86640f (patch)
tree09fecd747f45985d6f80be8954b3241fe310110c
parent130c5ce716c9bfd1c2a2ec840a746eb7ff9ce1e6 (diff)
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oprofile, dcookies: Fix possible circular locking dependency
The lockdep warning below detects a possible A->B/B->A locking dependency of mm->mmap_sem and dcookie_mutex. The order in sync_buffer() is mm->mmap_sem/dcookie_mutex, while in sys_lookup_dcookie() it is vice versa. Fixing it in sys_lookup_dcookie() by unlocking dcookie_mutex before copy_to_user(). oprofiled/4432 is trying to acquire lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810b444b>] might_fault+0x53/0xa3 but task is already holding lock: (dcookie_mutex){+.+.+.}, at: [<ffffffff81124d28>] sys_lookup_dcookie+0x45/0x149 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (dcookie_mutex){+.+.+.}: [<ffffffff8106557f>] lock_acquire+0xf8/0x11e [<ffffffff814634f0>] mutex_lock_nested+0x63/0x309 [<ffffffff81124e5c>] get_dcookie+0x30/0x144 [<ffffffffa0000fba>] sync_buffer+0x196/0x3ec [oprofile] [<ffffffffa0001226>] task_exit_notify+0x16/0x1a [oprofile] [<ffffffff81467b96>] notifier_call_chain+0x37/0x63 [<ffffffff8105803d>] __blocking_notifier_call_chain+0x50/0x67 [<ffffffff81058068>] blocking_notifier_call_chain+0x14/0x16 [<ffffffff8105a718>] profile_task_exit+0x1a/0x1c [<ffffffff81039e8f>] do_exit+0x2a/0x6fc [<ffffffff8103a5e4>] do_group_exit+0x83/0xae [<ffffffff8103a626>] sys_exit_group+0x17/0x1b [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b -> #0 (&mm->mmap_sem){++++++}: [<ffffffff81064dfb>] __lock_acquire+0x1085/0x1711 [<ffffffff8106557f>] lock_acquire+0xf8/0x11e [<ffffffff810b4478>] might_fault+0x80/0xa3 [<ffffffff81124de7>] sys_lookup_dcookie+0x104/0x149 [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b other info that might help us debug this: 1 lock held by oprofiled/4432: #0: (dcookie_mutex){+.+.+.}, at: [<ffffffff81124d28>] sys_lookup_dcookie+0x45/0x149 stack backtrace: Pid: 4432, comm: oprofiled Not tainted 2.6.39-00008-ge5a450d #9 Call Trace: [<ffffffff81063193>] print_circular_bug+0xae/0xbc [<ffffffff81064dfb>] __lock_acquire+0x1085/0x1711 [<ffffffff8102ef13>] ? get_parent_ip+0x11/0x42 [<ffffffff810b444b>] ? might_fault+0x53/0xa3 [<ffffffff8106557f>] lock_acquire+0xf8/0x11e [<ffffffff810b444b>] ? might_fault+0x53/0xa3 [<ffffffff810d7d54>] ? path_put+0x22/0x27 [<ffffffff810b4478>] might_fault+0x80/0xa3 [<ffffffff810b444b>] ? might_fault+0x53/0xa3 [<ffffffff81124de7>] sys_lookup_dcookie+0x104/0x149 [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b References: https://bugzilla.kernel.org/show_bug.cgi?id=13809 Cc: <stable@kernel.org> # .27+ Signed-off-by: Robert Richter <robert.richter@amd.com>
-rw-r--r--fs/dcookies.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/dcookies.c b/fs/dcookies.c
index a21cabdbd87..dda0dc702d1 100644
--- a/fs/dcookies.c
+++ b/fs/dcookies.c
@@ -178,6 +178,8 @@ SYSCALL_DEFINE(lookup_dcookie)(u64 cookie64, char __user * buf, size_t len)
/* FIXME: (deleted) ? */
path = d_path(&dcs->path, kbuf, PAGE_SIZE);
+ mutex_unlock(&dcookie_mutex);
+
if (IS_ERR(path)) {
err = PTR_ERR(path);
goto out_free;
@@ -194,6 +196,7 @@ SYSCALL_DEFINE(lookup_dcookie)(u64 cookie64, char __user * buf, size_t len)
out_free:
kfree(kbuf);
+ return err;
out:
mutex_unlock(&dcookie_mutex);
return err;