On Mon 02-10-17 19:15:19, Shakeel Butt wrote:
> The user space application can directly trigger the allocations
> from eventpoll_epi and eventpoll_pwq slabs. A buggy or malicious
> application can consume a significant amount of system memory by
> triggering such allocations. Indeed we have seen in production
> where a buggy application was leaking the epoll references and
> causing a burst of eventpoll_epi and eventpoll_pwq slab
> allocations. This patch opt-in the charging of eventpoll_epi
> and eventpoll_pwq slabs.
I am not objecting to the patch I would just like to understand the
runaway case. ep_insert seems to limit the maximum number of watches to
max_user_watches which should be ~4% of lowmem if I am following the
code properly. pwq_cache should be bound by the number of watches as
well, or am I misunderstanding the code?
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> ---
> fs/eventpoll.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 2fabd19cdeea..a45360444895 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -2329,11 +2329,11 @@ static int __init eventpoll_init(void)
>
> /* Allocates slab cache used to allocate "struct epitem" items */
> epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
> - 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
> + 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
>
> /* Allocates slab cache used to allocate "struct eppoll_entry" */
> pwq_cache = kmem_cache_create("eventpoll_pwq",
> - sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
> + sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
>
> return 0;
> }
> --
> 2.14.2.822.g60be5d43e6-goog
--
Michal Hocko
SUSE Labs
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