linux-kernel - Re: [2.6.34-git8][regression] massive polling problems with udevd and other processes

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Message-ID: <AANLkTilIpEo3LSE9FuGpTh3OKHT12_v2rHRWUXRc_QhC@mail.gmail.com>
Date:	Wed, 26 May 2010 23:01:40 +0200
From:	Alessandro Suardi <alessandro.suardi@...il.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	Eric Paris <eparis@...isplace.org>,
	Al Viro <viro@...iv.linux.org.uk>, walt <w41ter@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6.34-git8][regression] massive polling problems with udevd and 
	other processes

On Mon, May 24, 2010 at 1:49 AM, Eric Paris <eparis@...hat.com> wrote:
> On Sun, 2010-05-23 at 22:20 +0200, Alessandro Suardi wrote:
>> On Sun, May 23, 2010 at 1:25 AM, Eric Paris <eparis@...hat.com> wrote:
>
>> > I'm feeling like this is a udev bug, but the only fix is going to be to
>> > revert and paper over anything else that has problems with
>> > (mode & S_IFMNT) == 0
>> >
>> > -Eric
>
>> [root@...f ~]# cat udevd.proc.pid.fd.out
>> lr-x------. 1 root root 64 2010-05-23 22:15 6 -> anon_inode:inotify
>> lrwx------. 1 root root 64 2010-05-23 22:15 7 -> anon_inode:[signalfd]
>
>> [root@...f ~]# head -30 udevd.strace.log
>> Process 1734 attached - interrupt to quit
>> poll([{fd=4, events=POLLIN}, {fd=5, events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 5, 3000) = 1 ([{fd=6, revents=POLLIN}])
>> ioctl(6, FIONREAD, [0])                 = 0
>
> Well at least I see what is wrong.  Before the change ioctl(FIONREAD)
> would go down this code path:
>
> sys_ioctl()
>  do_vfs_ioctl()
>    vfs_ioctl()
>      filp->f_ops->ioctl()
>        inotify_ioctl()
>          returns the answer.
>
> After the change we instead get:
>
> sys_ioctl()
>  do_vfs_ioctl()
>    file_ioctl()
>      which would return put_user(i_size_read(inode) - filp->f_pos, p)
>
> If there is no rule that all inodes must be of a known S_IFMNT then I
> guess the best fix is to just revert and I'll fix up the symptoms.  If
> there is such an unwritten rule (which seems perfectly reasonable) we
> can either special case the anon_inode to push FIONREAD down to
> vfs_ioctl or move FIONREAD down to vfs_ioctl and force everyone else to
> implement it.
>
> Al?  Maybe you have better ideas?

2.6.34-git11 with F12's just-updated udev-145-21.fc12.x86_64 is still
 exposing this issue... ATM I'm simply killing udevd right after booting,
 but it's definitely not an optimal solution.

If more thought to a better fix is required, perhaps it's best for now to
 just revert the change that introduced the regression.

thanks,

--alessandro

 "There's always a siren singing you to shipwreck"

   (Radiohead, "There There")
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