linux-kernel - Bug 71331 - mlock yields processor to lower priority process

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Fri, 21 Mar 2014 23:02:49 +0300
From:	Artem Fetishev <artem_fetishev@...m.com>
To:	<peterz@...radead.org>, <jmdavis@...k.com>,
	<kosaki.motohiro@...fujitsu.com>
CC:	<linux-kernel@...r.kernel.org>
Subject: Bug 71331 - mlock yields processor to lower priority process

Hi all,

I am looking at a use-case when a real-time task (B) of higher priority is sometimes preempted by another real-time task (A) of lower priority. Well, B is not really preempted. It calls mlockall() which forces task B to yield the CPU. Under certain conditions, mlockall() calls lru_add_drain_all() which schedules a deferred work and wants the calling task to wait until that work is complete by putting the task into TASK_UNINTERRUPTIBLE state and calling schedule_timeout().

Tasks utilize SCHED_FIFO policy.

See details here: https://bugzilla.kernel.org/show_bug.cgi?id=71331

Besides mlockall, there are other kernel paths which make use of lru_add_drain_all() and schedule_timeout(), so I guess there are bunch of other syscalls which may lead to the above use-case.

So the question is: is above use-case an expected behavior of real-time tasks or is it a bug in mlockall (i.e. it should not interrupt a real-time process)?

Thanks,
-Artem
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/