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

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Message-ID: <20120210150923.GA12322@redhat.com>
Date:	Fri, 10 Feb 2012 16:09:23 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <dvlasenk@...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, Oleg Nesterov wrote:
>
> Add CC's,
>
> On 02/10, Denys Vlasenko wrote:
> >
> > I recalled that I saw a spurious EINTR on strace attach.
> > I found time/inspiration to create an isolated testcase for it.
> > Already committed it to ptrace-tests.
> >
> > The code: skip all the cruft, read reproduce() function body.
> > It's quite straightforward.
> >
> > $ gcc -Wall -Os eintr-on-attach.c -oeintr-on-attach
> > $ ./eintr-on-attach 1;echo 1
> > bug: read was interrupted by attach, errno: Interrupted system call
>
> 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.

Oleg.

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