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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 18 Dec 2019 12:25:09 +0100
Subject: [PATCH] userfaultfd: Use a seqlock instead of seqcount
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.13-rt7.tar.xz
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>
---
fs/userfaultfd.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -61,7 +61,7 @@ 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 */
refcount_t refcount;
/* userfaultfd syscall flags */
@@ -1063,7 +1063,7 @@ static ssize_t userfaultfd_ctx_read(stru
* 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
@@ -1089,7 +1089,7 @@ static ssize_t userfaultfd_ctx_read(stru
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;
@@ -1262,11 +1262,11 @@ static __always_inline void wake_userfau
* 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);
}
@@ -1939,7 +1939,7 @@ static void init_once_userfaultfd_ctx(vo
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);
}
SYSCALL_DEFINE1(userfaultfd, int, flags)
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