[PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls

paulmck
2020-06-23T00:21:54Z

From: "Paul E. McKenney" <paulmck@kernel.org>

A large process running on a heavily loaded system can encounter the
following RCU CPU stall warning:

rcu: INFO: rcu_sched self-detected stall on CPU
rcu: \x093-....: (20998 ticks this GP) idle=4ea/1/0x4000000000000002 softirq=556558/556558 fqs=5190
\x09(t=21013 jiffies g=1005461 q=132576)
NMI backtrace for cpu 3
CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1
Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016
Call Trace:
<IRQ>
dump_stack+0x46/0x60
nmi_cpu_backtrace.cold.3+0x13/0x50
? lapic_can_unplug_cpu.cold.27+0x34/0x34
nmi_trigger_cpumask_backtrace+0xba/0xca
rcu_dump_cpu_stacks+0x99/0xc7
rcu_sched_clock_irq.cold.87+0x1aa/0x397
? tick_sched_do_timer+0x60/0x60
update_process_times+0x28/0x60
tick_sched_timer+0x37/0x70
__hrtimer_run_queues+0xfe/0x270
hrtimer_interrupt+0xf4/0x210
smp_apic_timer_interrupt+0x5e/0x120
apic_timer_interrupt+0xf/0x20
</IRQ>
RIP: 0010:kmem_cache_free+0x223/0x300
Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a 02 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 a8 03 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65
RSP: 0018:ffffc9000e8e3da8 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff13
RAX: 0000000000020000 RBX: ffff88861b9de960 RCX: 0000000000000030
RDX: fffffffffffe41e8 RSI: 000060777fe3a100 RDI: 000000000001be18
RBP: ffffea00186e7780 R08: ffffffffffffffff R09: ffffffffffffffff
R10: ffff88861b9dea28 R11: ffff88887ffde000 R12: ffffffff81230a1f
R13: ffff888854684dc0 R14: 0000000000000206 R15: ffff8888547dbc00
? remove_vma+0x4f/0x60
remove_vma+0x4f/0x60
exit_mmap+0xd6/0x160
mmput+0x4a/0x110
do_exit+0x278/0xae0
? syscall_trace_enter+0x1d3/0x2b0
? handle_mm_fault+0xaa/0x1c0
do_group_exit+0x3a/0xa0
__x64_sys_exit_group+0x14/0x20
do_syscall_64+0x42/0x100
entry_SYSCALL_64_after_hwframe+0x44/0xa9

And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run
for a very long time given a large process. This commit therefore adds
a cond_resched() to this loop, providing RCU any needed quiescent states.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
mm/mmap.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 59a4682..972f839 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm)
if (vma->vm_flags & VM_ACCOUNT)
nr_accounted += vma_pages(vma);
vma = remove_vma(vma);
+ cond_resched();
}
vm_unacct_memory(nr_accounted);
}
--
2.9.5