linux-kernel - Re: I finally prepared a testcase for read(inotify_fd) getting EINTR on PTRACE

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Message-ID: <4F3543AA.5040003@redhat.com>
Date:	Fri, 10 Feb 2012 17:19:54 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Eric Paris <eparis@...isplace.org>
Subject: Re: I finally prepared a testcase for read(inotify_fd) getting EINTR
 on PTRACE_ATTACH

On 02/10/2012 04:09 PM, Oleg Nesterov wrote:
> On 02/10, Oleg Nesterov wrote:
>> At first glance this looks obvious? I never used inotify and I never
>> looked into fs/notify/inotify/, but it seems that inotify_read() simply
>> returns -EINTR if signal_pending() and doesn't implement restarts.
>>
>> Probably this trivial change
>>
>> 	--- x/fs/notify/inotify/inotify_user.c
>> 	+++ x/fs/notify/inotify/inotify_user.c
>> 	@@ -264,7 +264,7 @@ static ssize_t inotify_read(struct file
>> 			ret = -EAGAIN;
>> 			if (file->f_flags&  O_NONBLOCK)
>> 				break;
>> 	-		ret = -EINTR;
>> 	+		ret = -ERESTARTSYS;
>> 			if (signal_pending(current))
>> 				break;
>>
>>
>> makes sense.
>
> except I meant -ERESTARTNOHAND to avoid the behavioural change.

I run-tested the fix. It works: testcase no longer fails
(modulo incorrect logic in the testcase which wase not working
properly on "no bug detected" code path. Fixed one:
http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/eintr-on-attach.c?cvsroot=systemtap
)

I'm not sure inotify really wants to deviate from other reads
and return -EINTR even for SA_RESTARTing signals. IOW:
I think -ERESTARTSYS here would be more correct than -ERESTARTNOHAND.

If -ERESTARTNOHAND is really what inotify people want, they need to
add a comment about it.

-- 
vda
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