The patch titled
Subject: memcg: make memcg->event_list_lock irqsafe
has been added to the -mm tree. Its filename is
memcg-make-memcg-event_list_lock-irqsafe.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/memcg-make-memcg-event_list_lock-irqsafe.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/memcg-make-memcg-event_list_lock-irqsafe.patch
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------------------------------------------------------
From: Shakeel Butt <shakeelb@xxxxxxxxxx>
Subject: memcg: make memcg->event_list_lock irqsafe
The memcg->event_list_lock is usually taken in the normal context but when
the userspace closes the corresponding eventfd, eventfd_release through
memcg_event_wake takes memcg->event_list_lock with interrupts disabled.
This is not an issue on its own but it creates a nested dependency from
eventfd_ctx->wqh.lock to memcg->event_list_lock.
Independently, for unrelated eventfd, eventfd_signal() can be called in
the irq context, thus making eventfd_ctx->wqh.lock an irq lock. For
example, FPGA DFL driver, VHOST VPDA driver and couple of VFIO drivers.
This will force memcg->event_list_lock to be an irqsafe lock as well.
One way to break the nested dependency between eventfd_ctx->wqh.lock and
memcg->event_list_lock is to add an indirection. However the simplest
solution would be to make memcg->event_list_lock irqsafe. This is cgroup
v1 feature, is in maintenance and may get deprecated in near future. So,
no need to add more code.
BTW this has been discussed previously [1] but there weren't irq users of
eventfd_signal() at the time.
[1] https://www.spinics.net/lists/cgroups/msg06248.html
Link: https://lkml.kernel.org/r/20210830172953.207257-1-shakeelb@xxxxxxxxxx
Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/mm/memcontrol.c~memcg-make-memcg-event_list_lock-irqsafe
+++ a/mm/memcontrol.c
@@ -4839,9 +4839,9 @@ static ssize_t memcg_write_event_control
vfs_poll(efile.file, &event->pt);
- spin_lock(&memcg->event_list_lock);
+ spin_lock_irq(&memcg->event_list_lock);
list_add(&event->list, &memcg->event_list);
- spin_unlock(&memcg->event_list_lock);
+ spin_unlock_irq(&memcg->event_list_lock);
fdput(cfile);
fdput(efile);
@@ -5268,12 +5268,12 @@ static void mem_cgroup_css_offline(struc
* Notify userspace about cgroup removing only after rmdir of cgroup
* directory to avoid race between userspace and kernelspace.
*/
- spin_lock(&memcg->event_list_lock);
+ spin_lock_irq(&memcg->event_list_lock);
list_for_each_entry_safe(event, tmp, &memcg->event_list, list) {
list_del_init(&event->list);
schedule_work(&event->remove);
}
- spin_unlock(&memcg->event_list_lock);
+ spin_unlock_irq(&memcg->event_list_lock);
page_counter_set_min(&memcg->memory, 0);
page_counter_set_low(&memcg->memory, 0);
_
Patches currently in -mm which might be from shakeelb@xxxxxxxxxx are
writeback-memcg-simplify-cgroup_writeback_by_id.patch
memcg-switch-lruvec-stats-to-rstat.patch
memcg-infrastructure-to-flush-memcg-stats.patch
memcg-infrastructure-to-flush-memcg-stats-v5.patch
memcg-cleanup-racy-sum-avoidance-code.patch
memcg-make-memcg-event_list_lock-irqsafe.patch
