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From: zanussi@kernel.org
To: LKML <linux-kernel@vger.kernel.org>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>, John Kacur <jkacur@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Daniel Wagner <wagi@monom.org>, Tom Zanussi <zanussi@kernel.org>
Subject: [PATCH RT 19/25] userfaultfd: Use a seqlock instead of seqcount
Date: Fri, 21 Feb 2020 15:24:47 -0600	[thread overview]
Message-ID: <889f5b989b28eb7b29f21092432948cd12d97c48.1582320278.git.zanussi@kernel.org> (raw)
In-Reply-To: <cover.1582320278.git.zanussi@kernel.org>
In-Reply-To: <cover.1582320278.git.zanussi@kernel.org>

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

v4.14.170-rt75-rc1 stable review patch.
If anyone has any objections, please let me know.

-----------


[ Upstream commit dc952a564d02997330654be9628bbe97ba2a05d3 ]

On RT write_seqcount_begin() disables preemption which leads to warning
in add_wait_queue() while the spinlock_t is acquired.
The waitqueue can't be converted to swait_queue because
userfaultfd_wake_function() is used as a custom wake function.

Use seqlock instead seqcount to avoid the preempt_disable() section
during add_wait_queue().

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
 fs/userfaultfd.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index e2b2196fd942..71886a8e8f71 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -51,7 +51,7 @@ struct userfaultfd_ctx {
 	/* waitqueue head for events */
 	wait_queue_head_t event_wqh;
 	/* a refile sequence protected by fault_pending_wqh lock */
-	struct seqcount refile_seq;
+	seqlock_t refile_seq;
 	/* pseudo fd refcounting */
 	atomic_t refcount;
 	/* userfaultfd syscall flags */
@@ -1047,7 +1047,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
 			 * waitqueue could become empty if this is the
 			 * only userfault.
 			 */
-			write_seqcount_begin(&ctx->refile_seq);
+			write_seqlock(&ctx->refile_seq);
 
 			/*
 			 * The fault_pending_wqh.lock prevents the uwq
@@ -1073,7 +1073,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
 			list_del(&uwq->wq.entry);
 			__add_wait_queue(&ctx->fault_wqh, &uwq->wq);
 
-			write_seqcount_end(&ctx->refile_seq);
+			write_sequnlock(&ctx->refile_seq);
 
 			/* careful to always initialize msg if ret == 0 */
 			*msg = uwq->msg;
@@ -1246,11 +1246,11 @@ static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
 	 * sure we've userfaults to wake.
 	 */
 	do {
-		seq = read_seqcount_begin(&ctx->refile_seq);
+		seq = read_seqbegin(&ctx->refile_seq);
 		need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
 			waitqueue_active(&ctx->fault_wqh);
 		cond_resched();
-	} while (read_seqcount_retry(&ctx->refile_seq, seq));
+	} while (read_seqretry(&ctx->refile_seq, seq));
 	if (need_wakeup)
 		__wake_userfault(ctx, range);
 }
@@ -1915,7 +1915,7 @@ static void init_once_userfaultfd_ctx(void *mem)
 	init_waitqueue_head(&ctx->fault_wqh);
 	init_waitqueue_head(&ctx->event_wqh);
 	init_waitqueue_head(&ctx->fd_wqh);
-	seqcount_init(&ctx->refile_seq);
+	seqlock_init(&ctx->refile_seq);
 }
 
 /**
-- 
2.14.1


  parent reply	other threads:[~2020-02-21 21:26 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-21 21:24 [PATCH RT 00/25] Linux v4.14.170-rt75-rc1 zanussi
2020-02-21 21:24 ` [PATCH RT 01/25] Fix wrong-variable use in irq_set_affinity_notifier zanussi
2020-02-21 21:24 ` [PATCH RT 02/25] x86: preempt: Check preemption level before looking at lazy-preempt zanussi
2020-02-21 21:24 ` [PATCH RT 03/25] sched/deadline: Ensure inactive_timer runs in hardirq context zanussi
2020-02-24  8:33   ` Sebastian Andrzej Siewior
2020-02-25 14:50     ` Juri Lelli
2020-02-21 21:24 ` [PATCH RT 04/25] i2c: hix5hd2: Remove IRQF_ONESHOT zanussi
2020-02-21 21:24 ` [PATCH RT 05/25] i2c: exynos5: " zanussi
2020-02-21 21:24 ` [PATCH RT 06/25] sched: migrate_dis/enable: Use sleeping_lock…() to annotate sleeping points zanussi
2020-02-21 21:24 ` [PATCH RT 07/25] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus_ptr zanussi
2020-02-21 21:24 ` [PATCH RT 08/25] sched: Remove dead __migrate_disabled() check zanussi
2020-02-21 21:24 ` [PATCH RT 09/25] sched: migrate disable: Protect cpus_ptr with lock zanussi
2020-02-21 21:24 ` [PATCH RT 10/25] lib/smp_processor_id: Don't use cpumask_equal() zanussi
2020-02-21 21:24 ` [PATCH RT 11/25] futex: Make the futex_hash_bucket spinlock_t again and bring back its old state zanussi
2020-02-21 21:24 ` [PATCH RT 12/25] locking/rtmutex: Clean ->pi_blocked_on in the error case zanussi
2020-02-21 21:24 ` [PATCH RT 13/25] lib/ubsan: Don't seralize UBSAN report zanussi
2020-02-21 21:24 ` [PATCH RT 14/25] kmemleak: Change the lock of kmemleak_object to raw_spinlock_t zanussi
2020-02-21 21:24 ` [PATCH RT 15/25] sched: migrate_enable: Use select_fallback_rq() zanussi
2020-02-24  9:43   ` Sebastian Andrzej Siewior
2020-02-24 15:31     ` Tom Zanussi
2020-02-24 16:05       ` Sebastian Andrzej Siewior
2020-02-24 22:15         ` Scott Wood
2020-02-21 21:24 ` [PATCH RT 16/25] Revert "ARM: Initialize split page table locks for vector page" zanussi
2020-02-21 21:24 ` [PATCH RT 17/25] x86/fpu: Don't cache access to fpu_fpregs_owner_ctx zanussi
2020-02-24  8:55   ` Sebastian Andrzej Siewior
2020-02-24 15:12     ` Tom Zanussi
2020-02-21 21:24 ` [PATCH RT 18/25] locking: Make spinlock_t and rwlock_t a RCU section on RT zanussi
2020-02-21 21:24 ` zanussi [this message]
2020-02-24  9:03   ` [PATCH RT 19/25] userfaultfd: Use a seqlock instead of seqcount Sebastian Andrzej Siewior
2020-02-24 15:14     ` Tom Zanussi
2020-02-24 16:17     ` Steven Rostedt
2020-02-21 21:24 ` [PATCH RT 20/25] kmemleak: Cosmetic changes zanussi
2020-02-24  9:12   ` Sebastian Andrzej Siewior
2020-02-24 15:18     ` Tom Zanussi
2020-02-24 15:52       ` Sebastian Andrzej Siewior
2020-02-21 21:24 ` [PATCH RT 21/25] smp: Use smp_cond_func_t as type for the conditional function zanussi
2020-02-24  9:52   ` Sebastian Andrzej Siewior
2020-02-24 15:34     ` Tom Zanussi
2020-02-21 21:24 ` [PATCH RT 22/25] mm/memcontrol: Move misplaced local_unlock_irqrestore() zanussi
2020-02-24  9:55   ` Sebastian Andrzej Siewior
2020-02-21 21:24 ` [PATCH RT 23/25] locallock: Include header for the `current' macro zanussi
2020-02-21 21:24 ` [PATCH RT 24/25] sched: Provide migrate_disable/enable() inlines zanussi
2020-02-21 21:24 ` [PATCH RT 25/25] Linux 4.14.170-rt75-rc1 zanussi

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