Messages in this thread Patch in this message | | | Date | Wed, 8 Mar 2017 13:53:06 -0800 | From | "Paul E. McKenney" <> | Subject | [PATCH] clock: Fix smp_processor_id() in preemptible bug |
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The v4.11-rc1 kernel emits the following splat in some configurations:
[ 43.681891] BUG: using smp_processor_id() in preemptible [00000000] code: kworker/3:1/49 [ 43.682511] caller is debug_smp_processor_id+0x17/0x20 [ 43.682893] CPU: 0 PID: 49 Comm: kworker/3:1 Not tainted 4.11.0-rc1+ #1 [ 43.683382] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 [ 43.683497] Workqueue: events __clear_sched_clock_stable [ 43.683497] Call Trace: [ 43.683497] dump_stack+0x4f/0x69 [ 43.683497] check_preemption_disabled+0xd9/0xf0 [ 43.683497] debug_smp_processor_id+0x17/0x20 [ 43.683497] __clear_sched_clock_stable+0x11/0x60 [ 43.683497] process_one_work+0x146/0x430 [ 43.683497] worker_thread+0x126/0x490 [ 43.683497] kthread+0xfc/0x130 [ 43.683497] ? process_one_work+0x430/0x430 [ 43.683497] ? kthread_create_on_node+0x40/0x40 [ 43.683497] ? umh_complete+0x30/0x30 [ 43.683497] ? call_usermodehelper_exec_async+0x12a/0x130 [ 43.683497] ret_from_fork+0x29/0x40 [ 43.689244] sched_clock: Marking unstable (43688244724, 179505618)<-(43867750342, 0)
This happens because workqueue handlers run with preemption enabled by default and the new this_scd() function accesses per-CPU variables. This commit therefore disables preemption across this call to this_scd() and to the uses of the pointer that it returns. Lightly tested successfully on x86.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index a08795e21628..aa184bea1344 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -143,7 +143,7 @@ static void __set_sched_clock_stable(void) static void __clear_sched_clock_stable(struct work_struct *work) { - struct sched_clock_data *scd = this_scd(); + struct sched_clock_data *scd; /* * Attempt to make the stable->unstable transition continuous. @@ -154,7 +154,10 @@ static void __clear_sched_clock_stable(struct work_struct *work) * * Still do what we can. */ + preempt_disable(); + scd = this_scd(); gtod_offset = (scd->tick_raw + raw_offset) - (scd->tick_gtod); + preempt_enable(); printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", scd->tick_gtod, gtod_offset,
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