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

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Message-ID: <20140804192358.GA23283@redhat.com>
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.

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