From 750d857c682f4db60d14722d430c7ccc35070962 Mon Sep 17 00:00:00 2001 From: Robert Richter Date: Fri, 13 Aug 2010 16:29:04 +0200 Subject: [PATCH] oprofile: fix crash when accessing freed task structs This patch fixes a crash during shutdown reported below. The crash is caused by accessing already freed task structs. The fix changes the order for registering and unregistering notifier callbacks. All notifiers must be initialized before buffers start working. To stop buffer synchronization we cancel all workqueues, unregister the notifier callback and then flush all buffers. After all of this we finally can free all tasks listed. This should avoid accessing freed tasks. On 22.07.10 01:14:40, Benjamin Herrenschmidt wrote: > So the initial observation is a spinlock bad magic followed by a crash > in the spinlock debug code: > > [ 1541.586531] BUG: spinlock bad magic on CPU#5, events/5/136 > [ 1541.597564] Unable to handle kernel paging request for data at address 0x6b6b6b6b6b6b6d03 > > Backtrace looks like: > > spin_bug+0x74/0xd4 > ._raw_spin_lock+0x48/0x184 > ._spin_lock+0x10/0x24 > .get_task_mm+0x28/0x8c > .sync_buffer+0x1b4/0x598 > .wq_sync_buffer+0xa0/0xdc > .worker_thread+0x1d8/0x2a8 > .kthread+0xa8/0xb4 > .kernel_thread+0x54/0x70 > > So we are accessing a freed task struct in the work queue when > processing the samples. Reported-by: Benjamin Herrenschmidt Cc: stable@kernel.org Signed-off-by: Robert Richter --- drivers/oprofile/buffer_sync.c | 27 ++++++++++++++------------- drivers/oprofile/cpu_buffer.c | 2 -- 2 files changed, 14 insertions(+), 15 deletions(-) diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c index a9352b2c7ac4..b7e755f4178a 100644 --- a/drivers/oprofile/buffer_sync.c +++ b/drivers/oprofile/buffer_sync.c @@ -141,16 +141,6 @@ static struct notifier_block module_load_nb = { .notifier_call = module_load_notify, }; - -static void end_sync(void) -{ - end_cpu_work(); - /* make sure we don't leak task structs */ - process_task_mortuary(); - process_task_mortuary(); -} - - int sync_start(void) { int err; @@ -158,7 +148,7 @@ int sync_start(void) if (!zalloc_cpumask_var(&marked_cpus, GFP_KERNEL)) return -ENOMEM; - start_cpu_work(); + mutex_lock(&buffer_mutex); err = task_handoff_register(&task_free_nb); if (err) @@ -173,7 +163,10 @@ int sync_start(void) if (err) goto out4; + start_cpu_work(); + out: + mutex_unlock(&buffer_mutex); return err; out4: profile_event_unregister(PROFILE_MUNMAP, &munmap_nb); @@ -182,7 +175,6 @@ out3: out2: task_handoff_unregister(&task_free_nb); out1: - end_sync(); free_cpumask_var(marked_cpus); goto out; } @@ -190,11 +182,20 @@ 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); - end_sync(); + mutex_unlock(&buffer_mutex); + flush_scheduled_work(); + + /* make sure we don't leak task structs */ + process_task_mortuary(); + process_task_mortuary(); + free_cpumask_var(marked_cpus); } diff --git a/drivers/oprofile/cpu_buffer.c b/drivers/oprofile/cpu_buffer.c index 219f79e2210a..f179ac2ea801 100644 --- a/drivers/oprofile/cpu_buffer.c +++ b/drivers/oprofile/cpu_buffer.c @@ -120,8 +120,6 @@ void end_cpu_work(void) cancel_delayed_work(&b->work); } - - flush_scheduled_work(); } /* -- 2.20.1