From: Sebastian Andrzej Siewior 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 --- 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)