| Message ID | 1397777471-8280-1-git-send-email-kamal@canonical.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index ba6085d..8505ec4 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -166,7 +166,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb, struct percpu_counter *fbc; compute_batch_value(); - if (action != CPU_DEAD) + if (action != CPU_DEAD && action != CPU_DEAD_FROZEN) return NOTIFY_OK; cpu = (unsigned long)hcpu;
This is a note to let you know that I have just added a patch titled lib/percpu_counter.c: fix bad percpu counter state during suspend to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue This patch is scheduled to be released in version 3.8.13.22. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.8.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 53e56d356a4f811f49116a43ec59bbe840a0f533 Mon Sep 17 00:00:00 2001 From: Jens Axboe <axboe@fb.com> Date: Tue, 8 Apr 2014 16:04:12 -0700 Subject: lib/percpu_counter.c: fix bad percpu counter state during suspend commit e39435ce68bb4685288f78b1a7e24311f7ef939f upstream. I got a bug report yesterday from Laszlo Ersek in which he states that his kvm instance fails to suspend. Laszlo bisected it down to this commit 1cf7e9c68fe8 ("virtio_blk: blk-mq support") where virtio-blk is converted to use the blk-mq infrastructure. After digging a bit, it became clear that the issue was with the queue drain. blk-mq tracks queue usage in a percpu counter, which is incremented on request alloc and decremented when the request is freed. The initial hunt was for an inconsistency in blk-mq, but everything seemed fine. In fact, the counter only returned crazy values when suspend was in progress. When a CPU is unplugged, the percpu counters merges that CPU state with the general state. blk-mq takes care to register a hotcpu notifier with the appropriate priority, so we know it runs after the percpu counter notifier. However, the percpu counter notifier only merges the state when the CPU is fully gone. This leaves a state transition where the CPU going away is no longer in the online mask, yet it still holds private values. This means that in this state, percpu_counter_sum() returns invalid results, and the suspend then hangs waiting for abs(dead-cpu-value) requests to complete which of course will never happen. Fix this by clearing the state earlier, so we never have a case where the CPU isn't in online mask but still holds private state. This bug has been there since forever, I guess we don't have a lot of users where percpu counters needs to be reliable during the suspend cycle. Signed-off-by: Jens Axboe <axboe@fb.com> Reported-by: Laszlo Ersek <lersek@redhat.com> Tested-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- lib/percpu_counter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 1.9.1