linux-kernel - Re: [RFC][PATCH 4/7] inotify: Deal with nested sleeps

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

Date:	Mon, 4 Aug 2014 21:23:58 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, ilya.dryomov@...tank.com,
	umgwanakikbuti@...il.com, linux-kernel@...r.kernel.org,
	Eric Paris <eparis@...isplace.org>,
	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>
Subject: Re: [RFC][PATCH 4/7] inotify: Deal with nested sleeps

On 08/04, Peter Zijlstra wrote:
>
>  	while (1) {
> -		prepare_to_wait(&group->notification_waitq, &wait, TASK_INTERRUPTIBLE);
> -
>  		mutex_lock(&group->notification_mutex);

So yes, even these 2 lines look obviously buggy. Even if
fsnotify_add_notify_event()->wake_up(&group->notification_waitq) uses
TASK_NORMAL, so at least this can't miss an event.

It is too later for me, but I am wondering if we can do another thing.
Something like

		int state;

		prepare_to_wait(wait, TASK_INTERRUPTIBLE);

		PUSH(&wait, state);
		mutex_lock();
		mutex_unlock();
		POP(&wait, state);

and, ignoring all races, lack of barriers, etc

	#define PUSH(w, s)	s = current->state; current->state = RUNNING;

	#define POP(w, s)	current->state = WOKEN(w) ? RUNNING : s;

Probably not... just curious.

Oleg.

--
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/