From: Siddh Raman Pant via Linux-kernel-mentees <linux-kernel-mentees@lists.linuxfoundation.org>
To: Mauro Carvalho Chehab <mchehab@kernel.org>,
Randy Dunlap <rdunlap@infradead.org>,
David Howells <dhowells@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
"Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
Eric Dumazet <edumazet@google.com>,
Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
Eric Biggers <ebiggers@kernel.org>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-security-module <linux-security-module@vger.kernel.org>,
keyrings <keyrings@vger.kernel.org>,
linux-kernel-mentees
<linux-kernel-mentees@lists.linuxfoundation.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: [RESEND PATCH v2 2/2] kernel/watch_queue: NULL the dangling *pipe, and use it for clear check
Date: Wed, 21 Sep 2022 14:57:46 +0530 [thread overview]
Message-ID: <21ea7a96018db8f140d7c68ca75665064361ad1b.1663750794.git.code@siddh.me> (raw)
In-Reply-To: <cover.1663750794.git.code@siddh.me>
NULL the dangling pipe reference while clearing watch_queue.
If not done, a reference to a freed pipe remains in the watch_queue,
as this function is called before freeing a pipe in free_pipe_info()
(see line 834 of fs/pipe.c).
The sole use of wqueue->defunct is for checking if the watch queue has
been cleared, but wqueue->pipe is also NULLed while clearing.
Thus, wqueue->defunct is superfluous, as wqueue->pipe can be checked
for NULL. Hence, the former can be removed.
Signed-off-by: Siddh Raman Pant <code@siddh.me>
---
include/linux/watch_queue.h | 4 +---
kernel/watch_queue.c | 12 ++++++------
2 files changed, 7 insertions(+), 9 deletions(-)
diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
index 7f8b1f15634b..d72ad82a4435 100644
--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -55,7 +55,7 @@ struct watch_filter {
*
* @rcu: RCU head
* @filter: Filter to use on watches
- * @pipe: The pipe we're using as a buffer
+ * @pipe: The pipe we're using as a buffer, NULL when queue is cleared/closed
* @watches: Contributory watches
* @notes: Preallocated notifications
* @notes_bitmap: Allocation bitmap for notes
@@ -63,7 +63,6 @@ struct watch_filter {
* @lock: To serialize accesses and removes
* @nr_notes: Number of notes
* @nr_pages: Number of pages in notes[]
- * @defunct: True when queues closed
*/
struct watch_queue {
struct rcu_head rcu;
@@ -76,7 +75,6 @@ struct watch_queue {
spinlock_t lock;
unsigned int nr_notes;
unsigned int nr_pages;
- bool defunct;
};
/**
diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index a6f9bdd956c3..a70ddfd622ee 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -43,7 +43,7 @@ MODULE_LICENSE("GPL");
static inline bool lock_wqueue(struct watch_queue *wqueue)
{
spin_lock_bh(&wqueue->lock);
- if (unlikely(wqueue->defunct)) {
+ if (unlikely(!wqueue->pipe)) {
spin_unlock_bh(&wqueue->lock);
return false;
}
@@ -105,9 +105,6 @@ static bool post_one_notification(struct watch_queue *wqueue,
unsigned int head, tail, mask, note, offset, len;
bool done = false;
- if (!pipe)
- return false;
-
spin_lock_irq(&pipe->rd_wait.lock);
mask = pipe->ring_size - 1;
@@ -603,8 +600,11 @@ void watch_queue_clear(struct watch_queue *wqueue)
rcu_read_lock();
spin_lock_bh(&wqueue->lock);
- /* Prevent new notifications from being stored. */
- wqueue->defunct = true;
+ /*
+ * This pipe will get freed by the caller free_pipe_info().
+ * Removing this reference also prevents new notifications.
+ */
+ wqueue->pipe = NULL;
while (!hlist_empty(&wqueue->watches)) {
watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);
--
2.35.1
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next prev parent reply other threads:[~2022-09-21 9:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-21 9:27 [RESEND PATCH v2 0/2] watch_queue: Clean up some code Siddh Raman Pant via Linux-kernel-mentees
2022-09-21 9:27 ` [RESEND PATCH v2 1/2] include/linux/watch_queue: Improve documentation Siddh Raman Pant via Linux-kernel-mentees
2022-09-21 9:27 ` Siddh Raman Pant via Linux-kernel-mentees [this message]
-- strict thread matches above, loose matches on Subject: below --
2022-08-06 7:43 [PATCH v2 0/2] watch_queue: Clean up some code Siddh Raman Pant via Linux-kernel-mentees
2022-08-06 7:43 ` [PATCH v2 2/2] kernel/watch_queue: NULL the dangling *pipe, and use it for clear check Siddh Raman Pant via Linux-kernel-mentees
2022-09-01 20:06 ` [RESEND PATCH " Siddh Raman Pant via Linux-kernel-mentees
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