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| author | Xunlei Pang <xlpang@redhat.com> | 2017-03-23 15:56:08 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2017-04-04 11:44:05 +0200 |
| commit | e96a7705e7d3fef96aec9b590c63b2f6f7d2ba22 (patch) | |
| tree | fe346dcdb503a15812f8a8d63d6e010f4544c445 /include/linux/init_task.h | |
| parent | 2a1c6029940675abb2217b590512dbf691867ec4 (diff) | |
| download | lwn-e96a7705e7d3fef96aec9b590c63b2f6f7d2ba22.tar.gz lwn-e96a7705e7d3fef96aec9b590c63b2f6f7d2ba22.zip | |
sched/rtmutex/deadline: Fix a PI crash for deadline tasks
A crash happened while I was playing with deadline PI rtmutex.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
IP: [<ffffffff810eeb8f>] rt_mutex_get_top_task+0x1f/0x30
PGD 232a75067 PUD 230947067 PMD 0
Oops: 0000 [#1] SMP
CPU: 1 PID: 10994 Comm: a.out Not tainted
Call Trace:
[<ffffffff810b658c>] enqueue_task+0x2c/0x80
[<ffffffff810ba763>] activate_task+0x23/0x30
[<ffffffff810d0ab5>] pull_dl_task+0x1d5/0x260
[<ffffffff810d0be6>] pre_schedule_dl+0x16/0x20
[<ffffffff8164e783>] __schedule+0xd3/0x900
[<ffffffff8164efd9>] schedule+0x29/0x70
[<ffffffff8165035b>] __rt_mutex_slowlock+0x4b/0xc0
[<ffffffff81650501>] rt_mutex_slowlock+0xd1/0x190
[<ffffffff810eeb33>] rt_mutex_timed_lock+0x53/0x60
[<ffffffff810ecbfc>] futex_lock_pi.isra.18+0x28c/0x390
[<ffffffff810ed8b0>] do_futex+0x190/0x5b0
[<ffffffff810edd50>] SyS_futex+0x80/0x180
This is because rt_mutex_enqueue_pi() and rt_mutex_dequeue_pi()
are only protected by pi_lock when operating pi waiters, while
rt_mutex_get_top_task(), will access them with rq lock held but
not holding pi_lock.
In order to tackle it, we introduce new "pi_top_task" pointer
cached in task_struct, and add new rt_mutex_update_top_task()
to update its value, it can be called by rt_mutex_setprio()
which held both owner's pi_lock and rq lock. Thus "pi_top_task"
can be safely accessed by enqueue_task_dl() under rq lock.
Originally-From: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Xunlei Pang <xlpang@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170323150216.157682758@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/linux/init_task.h')
| -rw-r--r-- | include/linux/init_task.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 91d9049f0039..2c487e0879d5 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -181,6 +181,7 @@ extern struct cred init_cred; #ifdef CONFIG_RT_MUTEXES # define INIT_RT_MUTEXES(tsk) \ .pi_waiters = RB_ROOT, \ + .pi_top_task = NULL, \ .pi_waiters_leftmost = NULL, #else # define INIT_RT_MUTEXES(tsk) |