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SubjectRe: [Patch] Convert max_user_watches to long.
On Wed, 27 Oct 2010, Robin Holt wrote:

> On a 16TB machine, max_user_watches has an integer overflow. Convert it
> to use a long and handle the associated fallout.

I can't say I like adding an otherwise unused variable just to please
pretty-looking, but the compiler will take care of it.

Acked-by: Davide Libenzi <davidel@xmailserver.org>




> Signed-off-by: Robin Holt <holt@sgi.com>
> To: Andrew Morton <akpm@linux-foundation.org>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Davide Libenzi <davidel@xmailserver.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: Pekka Enberg <penberg@cs.helsinki.fi>
>
> ---
>
> fs/eventpoll.c | 20 ++++++++++++--------
> include/linux/sched.h | 2 +-
> 2 files changed, 13 insertions(+), 9 deletions(-)
>
> Index: pv1010933/fs/eventpoll.c
> ===================================================================
> --- pv1010933.orig/fs/eventpoll.c 2010-10-27 14:04:44.000000000 -0500
> +++ pv1010933/fs/eventpoll.c 2010-10-27 14:07:50.211457551 -0500
> @@ -220,7 +220,7 @@ struct ep_send_events_data {
> * Configuration options available inside /proc/sys/fs/epoll/
> */
> /* Maximum number of epoll watched descriptors, per user */
> -static int max_user_watches __read_mostly;
> +static long max_user_watches __read_mostly;
>
> /*
> * This mutex is used to serialize ep_free() and eventpoll_release_file().
> @@ -243,16 +243,18 @@ static struct kmem_cache *pwq_cache __re
>
> #include <linux/sysctl.h>
>
> -static int zero;
> +static long zero;
> +static long long_max = LONG_MAX;
>
> ctl_table epoll_table[] = {
> {
> .procname = "max_user_watches",
> .data = &max_user_watches,
> - .maxlen = sizeof(int),
> + .maxlen = sizeof(max_user_watches),
> .mode = 0644,
> - .proc_handler = proc_dointvec_minmax,
> + .proc_handler = proc_doulongvec_minmax,
> .extra1 = &zero,
> + .extra2 = &long_max,
> },
> { }
> };
> @@ -564,7 +566,7 @@ static int ep_remove(struct eventpoll *e
> /* At this point it is safe to free the eventpoll item */
> kmem_cache_free(epi_cache, epi);
>
> - atomic_dec(&ep->user->epoll_watches);
> + atomic_long_dec(&ep->user->epoll_watches);
>
> return 0;
> }
> @@ -900,11 +902,12 @@ static int ep_insert(struct eventpoll *e
> {
> int error, revents, pwake = 0;
> unsigned long flags;
> + long user_watches;
> struct epitem *epi;
> struct ep_pqueue epq;
>
> - if (unlikely(atomic_read(&ep->user->epoll_watches) >=
> - max_user_watches))
> + user_watches = atomic_long_read(&ep->user->epoll_watches);
> + if (unlikely(user_watches >= max_user_watches))
> return -ENOSPC;
> if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
> return -ENOMEM;
> @@ -968,7 +971,7 @@ static int ep_insert(struct eventpoll *e
>
> spin_unlock_irqrestore(&ep->lock, flags);
>
> - atomic_inc(&ep->user->epoll_watches);
> + atomic_long_inc(&ep->user->epoll_watches);
>
> /* We have to call this outside the lock */
> if (pwake)
> @@ -1422,6 +1425,7 @@ static int __init eventpoll_init(void)
> */
> max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
> EP_ITEM_COST;
> + BUG_ON(max_user_watches < 0);
>
> /* Initialize the structure used to perform safe poll wait head wake ups */
> ep_nested_calls_init(&poll_safewake_ncalls);
> Index: pv1010933/include/linux/sched.h
> ===================================================================
> --- pv1010933.orig/include/linux/sched.h 2010-10-27 14:04:44.000000000 -0500
> +++ pv1010933/include/linux/sched.h 2010-10-27 14:04:47.119415143 -0500
> @@ -666,7 +666,7 @@ struct user_struct {
> atomic_t inotify_devs; /* How many inotify devs does this user have opened? */
> #endif
> #ifdef CONFIG_EPOLL
> - atomic_t epoll_watches; /* The number of file descriptors currently watched */
> + atomic_long_t epoll_watches; /* The number of file descriptors currently watched */
> #endif
> #ifdef CONFIG_POSIX_MQUEUE
> /* protected by mq_lock */
>
>


- Davide




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