linux-kernel - [RFC PATCH 65/86] treewide: task_work: remove cond

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20231107230822.371443-9-ankur.a.arora@oracle.com>
Date:   Tue,  7 Nov 2023 15:08:01 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org,
        torvalds@...ux-foundation.org, paulmck@...nel.org,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, willy@...radead.org, mgorman@...e.de,
        jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
        bristot@...nel.org, mathieu.desnoyers@...icios.com,
        geert@...ux-m68k.org, glaubitz@...sik.fu-berlin.de,
        anton.ivanov@...bridgegreys.com, mattst88@...il.com,
        krypton@...ich-teichert.org, rostedt@...dmis.org,
        David.Laight@...LAB.COM, richard@....at, mjguzik@...il.com,
        Ankur Arora <ankur.a.arora@...cle.com>,
        Oleg Nesterov <oleg@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: [RFC PATCH 65/86] treewide: task_work: remove cond_resched()

The cond_resched() call was added in commit f341861fb0b7 ("task_work:
add a scheduling point in task_work_run()") because of softlockups
when processes with a large number of open sockets would exit.

Given the always-on PREEMPTION, we should be able to remove it
without much concern. However, task_work_run() does get called
from some "interesting" places: one of them being the
exit_to_user_loop() itself.

That means that if TIF_NEED_RESCHED (or TIF_NEED_RESCHED_LAZY) were
to be set once we were in a potentially long running task_work_run()
all, then we would ignore the need-resched flags and there would
be no call to schedule().

However, in that case, the next timer tick should cause rescheduling
in irqentry_exit_cond_resched(), since then the TIF_NEED_RESCHED flag
(even if the original flag were TIF_NEED_RESCHED_LAZY the tick would
upgrade that.)

Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 kernel/task_work.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 95a7e1b7f1da..6a891465c8e1 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -179,7 +179,6 @@ void task_work_run(void)
 			next = work->next;
 			work->func(work);
 			work = next;
-			cond_resched();
 		} while (work);
 	}
 }
-- 
2.31.1