si_meminfo() calls nr_blockdev_pages() that grabs bdev_lock, but it is
not safe to grab the lock from the hardirq context (the lock is never
taken with an _irqsave variant in block_dev.c). When taken from an
inappropriate context it easily causes the following deadlock:
- - - -
=================================
[ INFO: inconsistent lock state ]
3.2.0+ #1
---------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
(bdev_lock){?.+...}, at: [<ffffffff810f1017>] nr_blockdev_pages+0x17/0x70
{HARDIRQ-ON-W} state was registered at:
[<ffffffff81061b20>] mark_irqflags+0x140/0x1b0
[<ffffffff81062f03>] __lock_acquire+0x4c3/0x9c0
[<ffffffff810639c6>] lock_acquire+0x96/0xc0
[<ffffffff8131c58c>] _raw_spin_lock+0x2c/0x40
[<ffffffff810f1017>] nr_blockdev_pages+0x17/0x70
[<ffffffff81089ba8>] si_meminfo+0x38/0x60
[<ffffffff81675493>] eventpoll_init+0x11/0xa1
[<ffffffff8165eb40>] do_one_initcall+0x7a/0x12e
[<ffffffff8165ec8e>] kernel_init+0x9a/0x114
[<ffffffff8131e934>] kernel_thread_helper+0x4/0x10
irq event stamp: 135250
hardirqs last enabled at (135247): [<ffffffff81009897>] default_idle+0x27/0x50
hardirqs last disabled at (135248): [<ffffffff8131e1ab>] apic_timer_interrupt+0x6b/0x80
softirqs last enabled at (135250): [<ffffffff8103814e>] _local_bh_enable+0xe/0x10
softirqs last disabled at (135249): [<ffffffff81038665>] irq_enter+0x65/0x80
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(bdev_lock);
<Interrupt>
lock(bdev_lock);
*** DEADLOCK ***
no locks held by swapper/0/0.
- - - -
The patch fixes the issue by using totalram_pages instead of
si_meminfo().
p.s.
Note that VMEVENT_EATTR_NR_SWAP_PAGES type calls si_swapinfo(), which
has a very similar problem. But there is no easy way to fix it.
Do we have any use case for the VMEVENT_EATTR_NR_SWAP_PAGES event? If
not, I'd vote for removing it and thus keeping things simple.
Otherwise we would have two options:
1. Modify swap accounting for vmevent (either start grabbing
_irqsave variant of swapfile.c's swap_lock, or try to
make the accounting atomic);
2. Start using kthreads for vmevent_sample().
Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
---
The patch is for git://github.com/penberg/linux.git vmevent/core.
mm/vmevent.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/vmevent.c b/mm/vmevent.c
index 2342752..1375f9d 100644
--- a/mm/vmevent.c
+++ b/mm/vmevent.c
@@ -51,18 +51,18 @@ static bool vmevent_match(struct vmevent_watch *watch,
static void vmevent_sample(struct vmevent_watch *watch)
{
struct vmevent_watch_event event;
- struct sysinfo si;
int n = 0;
memset(&event, 0, sizeof(event));
event.nr_free_pages = global_page_state(NR_FREE_PAGES);
- si_meminfo(&si);
- event.nr_avail_pages = si.totalram;
+ event.nr_avail_pages = totalram_pages;
#ifdef CONFIG_SWAP
if (watch->config.event_attrs & VMEVENT_EATTR_NR_SWAP_PAGES) {
+ struct sysinfo si;
+
si_swapinfo(&si);
event.nr_swap_pages = si.totalswap;
}
--
1.7.7.6
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