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authorRobert Richter <robert.richter@amd.com>2011-05-26 18:39:35 +0200
committerRobert Richter <robert.richter@amd.com>2011-05-31 16:33:34 +0200
commit130c5ce716c9bfd1c2a2ec840a746eb7ff9ce1e6 (patch)
tree9d5ae217dd7236c73c12ee1bed9111ad6782acab /drivers/oprofile
parent6ac6519b93065625119a347be1cbcc1b89edb773 (diff)
downloadkernel-130c5ce716c9bfd1c2a2ec840a746eb7ff9ce1e6.tar.gz
oprofile: Fix locking dependency in sync_start()
This fixes the A->B/B->A locking dependency, see the warning below. The function task_exit_notify() is called with (task_exit_notifier) .rwsem set and then calls sync_buffer() which locks buffer_mutex. In sync_start() the buffer_mutex was set to prevent notifier functions to be started before sync_start() is finished. But when registering the notifier, (task_exit_notifier).rwsem is locked too, but now in different order than in sync_buffer(). In theory this causes a locking dependency, what does not occur in practice since task_exit_notify() is always called after the notifier is registered which means the lock is already released. However, after checking the notifier functions it turned out the buffer_mutex in sync_start() is unnecessary. This is because sync_buffer() may be called from the notifiers even if sync_start() did not finish yet, the buffers are already allocated but empty. No need to protect this with the mutex. So we fix this theoretical locking dependency by removing buffer_mutex in sync_start(). This is similar to the implementation before commit: 750d857 oprofile: fix crash when accessing freed task structs which introduced the locking dependency. Lockdep warning: oprofiled/4447 is trying to acquire lock: (buffer_mutex){+.+...}, at: [<ffffffffa0000e55>] sync_buffer+0x31/0x3ec [oprofile] but task is already holding lock: ((task_exit_notifier).rwsem){++++..}, at: [<ffffffff81058026>] __blocking_notifier_call_chain+0x39/0x67 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 ((task_exit_notifier).rwsem){++++..}: [<ffffffff8106557f>] lock_acquire+0xf8/0x11e [<ffffffff81463a2b>] down_write+0x44/0x67 [<ffffffff810581c0>] blocking_notifier_chain_register+0x52/0x8b [<ffffffff8105a6ac>] profile_event_register+0x2d/0x2f [<ffffffffa00013c1>] sync_start+0x47/0xc6 [oprofile] [<ffffffffa00001bb>] oprofile_setup+0x60/0xa5 [oprofile] [<ffffffffa00014e3>] event_buffer_open+0x59/0x8c [oprofile] [<ffffffff810cd3b9>] __dentry_open+0x1eb/0x308 [<ffffffff810cd59d>] nameidata_to_filp+0x60/0x67 [<ffffffff810daad6>] do_last+0x5be/0x6b2 [<ffffffff810dbc33>] path_openat+0xc7/0x360 [<ffffffff810dbfc5>] do_filp_open+0x3d/0x8c [<ffffffff810ccfd2>] do_sys_open+0x110/0x1a9 [<ffffffff810cd09e>] sys_open+0x20/0x22 [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b -> #0 (buffer_mutex){+.+...}: [<ffffffff81064dfb>] __lock_acquire+0x1085/0x1711 [<ffffffff8106557f>] lock_acquire+0xf8/0x11e [<ffffffff814634f0>] mutex_lock_nested+0x63/0x309 [<ffffffffa0000e55>] sync_buffer+0x31/0x3ec [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 other info that might help us debug this: 1 lock held by oprofiled/4447: #0: ((task_exit_notifier).rwsem){++++..}, at: [<ffffffff81058026>] __blocking_notifier_call_chain+0x39/0x67 stack backtrace: Pid: 4447, comm: oprofiled Not tainted 2.6.39-00007-gcf4d8d4 #10 Call Trace: [<ffffffff81063193>] print_circular_bug+0xae/0xbc [<ffffffff81064dfb>] __lock_acquire+0x1085/0x1711 [<ffffffffa0000e55>] ? sync_buffer+0x31/0x3ec [oprofile] [<ffffffff8106557f>] lock_acquire+0xf8/0x11e [<ffffffffa0000e55>] ? sync_buffer+0x31/0x3ec [oprofile] [<ffffffff81062627>] ? mark_lock+0x42f/0x552 [<ffffffffa0000e55>] ? sync_buffer+0x31/0x3ec [oprofile] [<ffffffff814634f0>] mutex_lock_nested+0x63/0x309 [<ffffffffa0000e55>] ? sync_buffer+0x31/0x3ec [oprofile] [<ffffffffa0000e55>] sync_buffer+0x31/0x3ec [oprofile] [<ffffffff81058026>] ? __blocking_notifier_call_chain+0x39/0x67 [<ffffffff81058026>] ? __blocking_notifier_call_chain+0x39/0x67 [<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 [<ffffffff81465031>] ? retint_swapgs+0xe/0x13 [<ffffffff8103a5e4>] do_group_exit+0x83/0xae [<ffffffff8103a626>] sys_exit_group+0x17/0x1b [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com> Cc: Carl Love <carll@us.ibm.com> Cc: <stable@kernel.org> # .36+ Signed-off-by: Robert Richter <robert.richter@amd.com>
Diffstat (limited to 'drivers/oprofile')
-rw-r--r--drivers/oprofile/buffer_sync.c8
1 files changed, 2 insertions, 6 deletions
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
index 04250aa16f51..f34b5b29fb95 100644
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -155,8 +155,6 @@ int sync_start(void)
if (!zalloc_cpumask_var(&marked_cpus, GFP_KERNEL))
return -ENOMEM;
- mutex_lock(&buffer_mutex);
-
err = task_handoff_register(&task_free_nb);
if (err)
goto out1;
@@ -173,7 +171,6 @@ int sync_start(void)
start_cpu_work();
out:
- mutex_unlock(&buffer_mutex);
return err;
out4:
profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
@@ -190,14 +187,13 @@ out1:
void sync_stop(void)
{
- /* flush buffers */
- mutex_lock(&buffer_mutex);
end_cpu_work();
unregister_module_notifier(&module_load_nb);
profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
task_handoff_unregister(&task_free_nb);
- mutex_unlock(&buffer_mutex);
+ barrier(); /* do all of the above first */
+
flush_cpu_work();
free_all_tasks();