linux-kernel - [tip: timers/core] wait: Fix __wait_event

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Message-ID: <165900503767.15455.17162045260398535319.tip-bot2@tip-bot2>
Date:   Thu, 28 Jul 2022 10:43:57 -0000
From:   "tip-bot2 for Juri Lelli" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Bruno Goncalves <bgoncalv@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: timers/core] wait: Fix __wait_event_hrtimeout for RT/DL tasks

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     cceeeb6a6d02e7b9a74ddd27a3225013b34174aa
Gitweb:        https://git.kernel.org/tip/cceeeb6a6d02e7b9a74ddd27a3225013b34174aa
Author:        Juri Lelli <juri.lelli@...hat.com>
AuthorDate:    Mon, 27 Jun 2022 11:50:51 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 28 Jul 2022 12:35:12 +02:00

wait: Fix __wait_event_hrtimeout for RT/DL tasks

Changes to hrtimer mode (potentially made by __hrtimer_init_sleeper on
PREEMPT_RT) are not visible to hrtimer_start_range_ns, thus not
accounted for by hrtimer_start_expires call paths. In particular,
__wait_event_hrtimeout suffers from this problem as we have, for
example:

fs/aio.c::read_events
  wait_event_interruptible_hrtimeout
    __wait_event_hrtimeout
      hrtimer_init_sleeper_on_stack <- this might "mode |= HRTIMER_MODE_HARD"
                                       on RT if task runs at RT/DL priority
        hrtimer_start_range_ns
          WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard)
          fires since the latter doesn't see the change of mode done by
          init_sleeper

Fix it by making __wait_event_hrtimeout call hrtimer_sleeper_start_expires,
which is aware of the special RT/DL case, instead of hrtimer_start_range_ns.

Reported-by: Bruno Goncalves <bgoncalv@...hat.com>
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...nel.org>
Reviewed-by: Valentin Schneider <vschneid@...hat.com>
Link: https://lore.kernel.org/r/20220627095051.42470-1-juri.lelli@redhat.com
---
 include/linux/wait.h |  9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 851e07d..58cfbf8 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -544,10 +544,11 @@ do {										\
 										\
 	hrtimer_init_sleeper_on_stack(&__t, CLOCK_MONOTONIC,			\
 				      HRTIMER_MODE_REL);			\
-	if ((timeout) != KTIME_MAX)						\
-		hrtimer_start_range_ns(&__t.timer, timeout,			\
-				       current->timer_slack_ns,			\
-				       HRTIMER_MODE_REL);			\
+	if ((timeout) != KTIME_MAX) {						\
+		hrtimer_set_expires_range_ns(&__t.timer, timeout,		\
+					current->timer_slack_ns);		\
+		hrtimer_sleeper_start_expires(&__t, HRTIMER_MODE_REL);		\
+	}									\
 										\
 	__ret = ___wait_event(wq_head, condition, state, 0, 0,			\
 		if (!__t.task) {						\