Messages in this thread | | | Date | Wed, 20 Mar 2024 13:09:07 -0400 | Subject | Re: [PATCH] mm/memcontrol: stop resize loop if limit was changed again | From | Waiman Long <> |
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On 3/20/24 06:03, Pavel Tikhomirov wrote: > In memory_max_write() we first set memcg->memory.max and only then > try to enforce it in loop. What if while we are in loop someone else > have changed memcg->memory.max but we are still trying to enforce > the old value? I believe this can lead to nasty consequence like getting > an oom on perfectly fine cgroup within it's limits or excess reclaim.
Concurrent write to the same cgroup control file is not possible as the underlying kernfs_open_file structure has a mutex that serialize access to the file. Concurrent write to different cgroup control files is possible, though.
Cheers, Longman
> > We also have exactly the same thing in memory_high_write(). > > So let's stop enforcing old limits if we already have a new ones. > > Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com> > --- > mm/memcontrol.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 61932c9215e7..81b303728491 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6769,6 +6769,9 @@ static ssize_t memory_high_write(struct kernfs_open_file *of, > unsigned long nr_pages = page_counter_read(&memcg->memory); > unsigned long reclaimed; > > + if (memcg->memory.high != high) > + break; > + > if (nr_pages <= high) > break; > > @@ -6817,6 +6820,9 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, > for (;;) { > unsigned long nr_pages = page_counter_read(&memcg->memory); > > + if (memcg->memory.max != max) > + break; > + > if (nr_pages <= max) > break; >
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