3.0-git19 snapshot

Add epoll patch until it gets upstreamed
Add trial patch to fix the scheduling while atomic issues around pidmap_init

1 files changed, 116 insertions, 0 deletions

diff --git a/epoll-fix-spurious-lockdep-warnings.patch b/epoll-fix-spurious-lockdep-warnings.patch
new file mode 100644
index 000000000..c163a86d7
--- /dev/null
+++ b/epoll-fix-spurious-lockdep-warnings.patch
@@ -0,0 +1,116 @@
+epoll can acquire multiple ep->mutex on multiple "struct eventpoll"s
+at once in the case where one epoll fd is monitoring another epoll
+fd. This is perfectly OK, since we're careful about the lock ordering,
+but causes spurious lockdep warnings. Annotate the recursion using
+mutex_lock_nested, and add a comment explaining the nesting rules for
+good measure.
+
+Reported-by: Paul Bolle <pebolle@tiscali.nl>
+Signed-off-by: Nelson Elhage <nelhage@nelhage.com>
+---
+ I've tested this on a synthetic epoll test case, that just adds e1 to
+ e2 and then does an epoll_wait(). I verified that it caused lockdep
+ problems on 3.0 and that this patch fixed it, but I haven't done more
+ extensive testing. Paul, are you able to test systemd against this?
+
+ fs/eventpoll.c |   25 ++++++++++++++++++-------
+ 1 files changed, 18 insertions(+), 7 deletions(-)
+
+diff --git a/fs/eventpoll.c b/fs/eventpoll.c
+index f9cfd16..0cb7bc6 100644
+--- a/fs/eventpoll.c
++++ b/fs/eventpoll.c
+@@ -76,6 +76,15 @@
+  * Events that require holding "epmutex" are very rare, while for
+  * normal operations the epoll private "ep->mtx" will guarantee
+  * a better scalability.
++ * It is possible to acquire multiple "ep->mtx"es at once in the case
++ * when one epoll fd is added to another. In this case, we always
++ * acquire the locks in the order of nesting (i.e. after epoll_ctl(e1,
++ * EPOLL_CTL_ADD, e2), e1->mtx will always be acquired before
++ * e2->mtx). Since we disallow cycles of epoll file descriptors, this
++ * ensures that the mutexes are well-ordered. In order to communicate
++ * this nesting to lockdep, when walking a tree of epoll file
++ * descriptors, we use the current recursion depth as the lockdep
++ * subkey.
+  */
+ 
+ /* Epoll private bits inside the event mask */
+@@ -464,13 +473,15 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
+  * @ep: Pointer to the epoll private data structure.
+  * @sproc: Pointer to the scan callback.
+  * @priv: Private opaque data passed to the @sproc callback.
++ * @depth: The current depth of recursive f_op->poll calls.
+  *
+  * Returns: The same integer error code returned by the @sproc callback.
+  */
+ static int ep_scan_ready_list(struct eventpoll *ep,
+ 			      int (*sproc)(struct eventpoll *,
+ 					   struct list_head *, void *),
+-			      void *priv)
++			      void *priv,
++			      int depth)
+ {
+ 	int error, pwake = 0;
+ 	unsigned long flags;
+@@ -481,7 +492,7 @@ static int ep_scan_ready_list(struct eventpoll *ep,
+ 	 * We need to lock this because we could be hit by
+ 	 * eventpoll_release_file() and epoll_ctl().
+ 	 */
+-	mutex_lock(&ep->mtx);
++	mutex_lock_nested(&ep->mtx, depth);
+ 
+ 	/*
+ 	 * Steal the ready list, and re-init the original one to the
+@@ -670,7 +681,7 @@ static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
+ 
+ static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
+ {
+-	return ep_scan_ready_list(priv, ep_read_events_proc, NULL);
++	return ep_scan_ready_list(priv, ep_read_events_proc, NULL, call_nests + 1);
+ }
+ 
+ static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
+@@ -737,7 +748,7 @@ void eventpoll_release_file(struct file *file)
+ 
+ 		ep = epi->ep;
+ 		list_del_init(&epi->fllink);
+-		mutex_lock(&ep->mtx);
++		mutex_lock_nested(&ep->mtx, 0);
+ 		ep_remove(ep, epi);
+ 		mutex_unlock(&ep->mtx);
+ 	}
+@@ -1134,7 +1145,7 @@ static int ep_send_events(struct eventpoll *ep,
+ 	esed.maxevents = maxevents;
+ 	esed.events = events;
+ 
+-	return ep_scan_ready_list(ep, ep_send_events_proc, &esed);
++	return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0);
+ }
+ 
+ static inline struct timespec ep_set_mstimeout(long ms)
+@@ -1267,7 +1278,7 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
+ 	struct rb_node *rbp;
+ 	struct epitem *epi;
+ 
+-	mutex_lock(&ep->mtx);
++	mutex_lock_nested(&ep->mtx, call_nests + 1);
+ 	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
+ 		epi = rb_entry(rbp, struct epitem, rbn);
+ 		if (unlikely(is_file_epoll(epi->ffd.file))) {
+@@ -1409,7 +1420,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
+ 	}
+ 
+ 
+-	mutex_lock(&ep->mtx);
++	mutex_lock_nested(&ep->mtx, 0);
+ 
+ 	/*
+ 	 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
+-- 
+1.7.4.1
+
+--
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