This is a note to let you know that I've just added the patch titled
sched/numa: Use down_read_trylock() for the mmap_sem
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: sched-numa-use-down_read_trylock-for-the-mmap_sem.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Tue Apr 10 10:31:53 CEST 2018
From: Vlastimil Babka vbabka@suse.cz Date: Mon, 15 May 2017 15:13:16 +0200 Subject: sched/numa: Use down_read_trylock() for the mmap_sem
From: Vlastimil Babka vbabka@suse.cz
[ Upstream commit 8655d5497735b288f8a9b458bd22e7d1bf95bb61 ]
A customer has reported a soft-lockup when running an intensive memory stress test, where the trace on multiple CPU's looks like this:
RIP: 0010:[<ffffffff810c53fe>] [<ffffffff810c53fe>] native_queued_spin_lock_slowpath+0x10e/0x190 ... Call Trace: [<ffffffff81182d07>] queued_spin_lock_slowpath+0x7/0xa [<ffffffff811bc331>] change_protection_range+0x3b1/0x930 [<ffffffff811d4be8>] change_prot_numa+0x18/0x30 [<ffffffff810adefe>] task_numa_work+0x1fe/0x310 [<ffffffff81098322>] task_work_run+0x72/0x90
Further investigation showed that the lock contention here is pmd_lock().
The task_numa_work() function makes sure that only one thread is let to perform the work in a single scan period (via cmpxchg), but if there's a thread with mmap_sem locked for writing for several periods, multiple threads in task_numa_work() can build up a convoy waiting for mmap_sem for read and then all get unblocked at once.
This patch changes the down_read() to the trylock version, which prevents the build up. For a workload experiencing mmap_sem contention, it's probably better to postpone the NUMA balancing work anyway. This seems to have fixed the soft lockups involving pmd_lock(), which is in line with the convoy theory.
Signed-off-by: Vlastimil Babka vbabka@suse.cz Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Acked-by: Rik van Riel riel@redhat.com Acked-by: Mel Gorman mgorman@techsingularity.net Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/20170515131316.21909-1-vbabka@suse.cz Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2223,7 +2223,8 @@ void task_numa_work(struct callback_head return;
- down_read(&mm->mmap_sem); + if (!down_read_trylock(&mm->mmap_sem)) + return; vma = find_vma(mm, start); if (!vma) { reset_ptenuma_scan(p);
Patches currently in stable-queue which might be from vbabka@suse.cz are
queue-4.4/sched-numa-use-down_read_trylock-for-the-mmap_sem.patch