linux-kernel - Re: Strange issues with epoll since 5.0

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Message-ID: <20190501022626.pcw3hbrzccn3iutm@dcvr>
Date:   Wed, 1 May 2019 02:26:26 +0000
From:   Eric Wong <e@...24.org>
To:     Deepa Dinamani <deepa.kernel@...il.com>
Cc:     Davidlohr Bueso <dave@...olabs.net>, Arnd Bergmann <arnd@...db.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jason Baron <jbaron@...mai.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Omar Kilani <omar.kilani@...il.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>
Subject: Re: Strange issues with epoll since 5.0

Eric Wong <e@...24.org> wrote:
> Deepa Dinamani <deepa.kernel@...il.com> wrote:
> > I'm not sure what the hang in the userspace is about. Is it because
> > the syscall did not return an error or the particular signal was
> > blocked etc.
> 
> Uh, ok; that's less comforting.

Nevermind, I think I understand everything, now.  epoll_pwait
never set errno without our patch.

cmogstored does this in notify.c:

	/* wait_intr calls epoll_pwait: */
        mfd = mog_idleq_wait_intr(mog_notify_queue, timeout);
        if (mfd)
                notify_queue_step(mfd);
        else if (errno == EINTR) /* EINTR fails to be noticed */
                note_run();