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epoll: rename global epmutex

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As of 4f04cbaf128 ("epoll: use refcount to reduce ep_mutex contention"),
this lock is now specific to nesting cases - inserting an epoll fd onto
another epoll fd.  Rename the lock to be less generic.

Link: https://lkml.kernel.org/r/20230411234159.20421-1-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Davidlohr Bueso 2023-04-11 16:41:59 -07:00 committed by Andrew Morton
parent 5a10562bde
commit d4cb626d6f
1 changed files with 11 additions and 11 deletions
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22
fs/eventpoll.c
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@ -43,7 +43,7 @@
* LOCKING:
* There are three level of locking required by epoll :
*
* 1) epmutex (mutex)
* 1) epnested_mutex (mutex)
* 2) ep->mtx (mutex)
* 3) ep->lock (rwlock)
*
@ -57,8 +57,8 @@
* we need a lock that will allow us to sleep. This lock is a
* mutex (ep->mtx). It is acquired during the event transfer loop,
* during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
* The epmutex is acquired when inserting an epoll fd onto another epoll
* fd. We do this so that we walk the epoll tree and ensure that this
* The epnested_mutex is acquired when inserting an epoll fd onto another
* epoll fd. We do this so that we walk the epoll tree and ensure that this
* insertion does not create a cycle of epoll file descriptors, which
* could lead to deadlock. We need a global mutex to prevent two
* simultaneous inserts (A into B and B into A) from racing and
@ -74,9 +74,9 @@
* of epoll file descriptors, we use the current recursion depth as
* the lockdep subkey.
* It is possible to drop the "ep->mtx" and to use the global
* mutex "epmutex" (together with "ep->lock") to have it working,
* mutex "epnested_mutex" (together with "ep->lock") to have it working,
* but having "ep->mtx" will make the interface more scalable.
* Events that require holding "epmutex" are very rare, while for
* Events that require holding "epnested_mutex" are very rare, while for
* normal operations the epoll private "ep->mtx" will guarantee
* a better scalability.
*/
@ -248,7 +248,7 @@ struct ep_pqueue {
static long max_user_watches __read_mostly;
/* Used for cycles detection */
static DEFINE_MUTEX(epmutex);
static DEFINE_MUTEX(epnested_mutex);
static u64 loop_check_gen = 0;
@ -263,7 +263,7 @@ static struct kmem_cache *pwq_cache __read_mostly;
/*
* List of files with newly added links, where we may need to limit the number
* of emanating paths. Protected by the epmutex.
* of emanating paths. Protected by the epnested_mutex.
*/
struct epitems_head {
struct hlist_head epitems;
@ -1337,7 +1337,7 @@ static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
* is connected to n file sources. In this case each file source has 1 path
* of length 1. Thus, the numbers below should be more than sufficient. These
* path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
* and delete can't add additional paths. Protected by the epmutex.
* and delete can't add additional paths. Protected by the epnested_mutex.
*/
static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
static int path_count[PATH_ARR_SIZE];
@ -2167,7 +2167,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
* We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
* the epoll file descriptor is attaching directly to a wakeup source,
* unless the epoll file descriptor is nested. The purpose of taking the
* 'epmutex' on add is to prevent complex toplogies such as loops and
* 'epnested_mutex' on add is to prevent complex toplogies such as loops and
* deep wakeup paths from forming in parallel through multiple
* EPOLL_CTL_ADD operations.
*/
@ -2178,7 +2178,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
if (READ_ONCE(f.file->f_ep) || ep->gen == loop_check_gen ||
is_file_epoll(tf.file)) {
mutex_unlock(&ep->mtx);
error = epoll_mutex_lock(&epmutex, 0, nonblock);
error = epoll_mutex_lock(&epnested_mutex, 0, nonblock);
if (error)
goto error_tgt_fput;
loop_check_gen++;
@ -2239,7 +2239,7 @@ error_tgt_fput:
if (full_check) {
clear_tfile_check_list();
loop_check_gen++;
mutex_unlock(&epmutex);
mutex_unlock(&epnested_mutex);
}
fdput(tf);