lkml.org 
[lkml]   [2019]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH RT] userfaultfd: Use a seqlock instead of seqcount
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().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
fs/userfaultfd.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index f9fd18670e22d..92871bee05b39 100644
--- 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(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
@@ -1089,7 +1089,7 @@ 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;
@@ -1262,11 +1262,11 @@ 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);
}
@@ -1935,7 +1935,7 @@ 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);
}

SYSCALL_DEFINE1(userfaultfd, int, flags)
--
2.24.0
\
 
 \ /
  Last update: 2019-12-18 17:58    [W:0.047 / U:8.784 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site