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

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Message-Id: <20100413063013.A0759B06B@magilla.sf.frob.com>
Date:	Mon, 12 Apr 2010 23:30:13 -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, /proc/pid/status can report the intermediate state, I even sent
> the updated changelog to document this.
> 
> But if you are not sure this is OK, I am worried. Do you think we should
> drop this patch? If yes, I won't argue.

I'm not dead-set against it, but I am hesitant.  My inclination is not to
remove any previous userland atomicity guarantees with regard to observable
signal state in any form.  At least, don't do that in part of a whole
cleanup flurry where it is intermixed with lots of changes that really are
pure cleanup with absolutely no userland-observable change.  If it really
helps to fragment what was atomic before, then we can consider it.  But
let's not be in a hurry.

David mentioned that users who do multiple reads due to using tiny buffers
already don't get atomic sampling.  That is certainly true but I don't
think it's relevant.  It is completely reliable that you can easily
allocate a buffer big enough to get all the Sig* fields on the first read,
and any user program that might care about the coherence of the data,
by definition, is already doing that.

Thanks,
Roland
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