Groups > linux.kernel > #1731984

Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion

From	Jaegeuk Kim <jaegeuk@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion
Date	2017-09-14 01:40 +0200
Message-ID	<uppqa-5wg-7@gated-at.bofh.it> (permalink)
References	<upmiC-3zs-21@gated-at.bofh.it> <upoX7-5ky-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

Hi Al,

On 09/14, Al Viro wrote:
> On Wed, Sep 13, 2017 at 01:09:41PM -0700, Jaegeuk Kim wrote:
> > +	if (!retval && (flags & UMOUNT_WAIT)) {
> > +		if (likely(!(current->flags & PF_KTHREAD)))
> > +			task_work_run();
> 
> This is complete crap.  The same damn thing will be done by
> caller of sys_umount() pretty much immediately afterwards.
> I'm not sure what it is that you are trying to paper over,
> but this is just plain wrong.

Okay.

> What _is_ the semantics of UMOUNT_WAIT?  What does it guarantee,
> and what would be supplying it to umount(2)?

When android tries to reboot the system, it calls umount(2) without any flag.
Then, mntput_no_expire() will add delayed_mntput_work() which finally does
cleanup_mnt() later. In the mean time, android proceeded to shutdown all
the UFS devices, but filesystem would be still alive and tries to trigger
some I/Os. At this moment, I'd like to avoid EIO, since ext4 can issue kernel
panic because of error=panic.

So, what I'm trying to do is 1) adding a flag to wait for umount() completion,
2) issuing umount(2) with UMOUNT_WAIT in android. Then, it can guarantee there'd
be no I/Os after sucessful umount().

Could you please correct me?

Thanks,

Thread

[PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-13 22:20 +0200
  Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 01:10 +0200
    Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-14 01:40 +0200
      Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 01:50 +0200
        Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-14 03:20 +0200
          Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 03:40 +0200
            Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 20:40 +0200
              Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-14 21:20 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-15 02:20 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-15 04:10 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-15 05:50 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-15 06:30 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-15 20:50 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Theodore Ts'o <tytso@mit.edu> - 2017-09-16 00:20 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-16 01:30 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-16 01:50 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-19 18:00 +0200
                Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Amir Goldstein <amir73il@gmail.com> - 2017-09-16 09:20 +0200
  Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-20 19:40 +0200
    Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-20 20:40 +0200
      Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 02:40 +0200
        Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-21 04:50 +0200
          Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 07:10 +0200
            Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Theodore Ts'o <tytso@mit.edu> - 2017-09-21 17:00 +0200
              Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount  completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 19:20 +0200
    Re: [PATCH v3] vfs: introduce UMOUNT_WAIT to wait for  delayed_fput/mntput completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 20:30 +0200

csiph-web