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    Subject[PATCH 4.9 099/212] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls
    Date
    From: Paul E. McKenney <paulmck@kernel.org>

    [ Upstream commit 0a3b3c253a1eb2c7fe7f34086d46660c909abeb3 ]

    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: 3-....: (20998 ticks this GP) idle=4ea/1/0x4000000000000002 softirq=556558/556558 fqs=5190
    (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>
    Reviewed-by: Shakeel Butt <shakeelb@google.com>
    Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    mm/mmap.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/mm/mmap.c b/mm/mmap.c
    index d221266d100f4..7109f886e739e 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -3018,6 +3018,7 @@ 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);
    }
    --
    2.25.1


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