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Sun, 03 Dec 2023 11:33:13 -0800 (PST) From: Yury Norov To: linux-kernel@vger.kernel.org, Christian Brauner , David Howells , Siddh Raman Pant , Yury Norov , Dave Airlie , David Disseldorp , Philipp Stanner , Nick Alcock Cc: Jan Kara , Mirsad Todorovac , Matthew Wilcox , Rasmus Villemoes , Andy Shevchenko , Maxim Kuvyrkov , Alexey Klimov , Bart Van Assche , Sergey Shtylyov Subject: [PATCH v2 04/35] watch_queue: use atomic find_bit() in post_one_notification() Date: Sun, 3 Dec 2023 11:32:36 -0800 Message-Id: <20231203193307.542794-3-yury.norov@gmail.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231203193307.542794-1-yury.norov@gmail.com> References: <20231203192422.539300-1-yury.norov@gmail.com> <20231203193307.542794-1-yury.norov@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-0.6 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on howler.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (howler.vger.email [0.0.0.0]); Sun, 03 Dec 2023 11:33:30 -0800 (PST) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1784290491120209763 X-GMAIL-MSGID: 1784290491120209763 post_one_notification() searches for a set bit in wqueue->notes_bitmap, and after some housekeeping work clears it, firing a BUG() if someone else cleared the bit in-between. We can allocate the bit atomically with an atomic find_and_clear_bit(), and remove the BUG() possibility entirely. Signed-off-by: Yury Norov --- kernel/watch_queue.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index 778b4056700f..07edd4a2b463 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -112,7 +112,7 @@ static bool post_one_notification(struct watch_queue *wqueue, if (pipe_full(head, tail, pipe->ring_size)) goto lost; - note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes); + note = find_and_clear_bit(wqueue->notes_bitmap, wqueue->nr_notes); if (note >= wqueue->nr_notes) goto lost; @@ -133,10 +133,6 @@ static bool post_one_notification(struct watch_queue *wqueue, buf->flags = PIPE_BUF_FLAG_WHOLE; smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */ - if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { - spin_unlock_irq(&pipe->rd_wait.lock); - BUG(); - } wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM); done = true;