linux-kernel - Re: [PATCH -mm 3/3] proc: make task

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Date:	Fri,  9 Apr 2010 12:59:36 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 3/3] proc: make task_sig() lockless

> Yes. From the changelog:
> 
> 	Of course, this means we read pending/blocked/etc nonatomically,
> 	but I hope this is OK for fs/proc.
> 
> But I don't think the returned data could be "really" inconsistent
> from the /bin/ps pov. Yes, it is possible that, say, some signal is
> seen as both pending and ignored without ->siglock. Or we can report
> user->sigpending != 0 while pending/shpending are empty.
> 
> But this looks harmless to me. We never guaranteed /proc/pid/status
> can't report the "intermediate" state, and I don't think we can
> confuse the user-space.
> 
> Do you agree? Or do you think this can make problems ?

I'm not so sure.  Operations like sigprocmask and sigaction really have
always been entirely atomic from the userland perspective before.  Now it
becomes possible to read from /proc e.g. a blocked set that never existed
as such (one word updated by sigprocmask but not yet the next word).


Thanks,
Roland
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