Re: [PATCH 0/13 v2] block: Fix block device shutdown related races

[Omar Sandoval <osandov@osandov.com>]

On Wed, Feb 22, 2017 at 11:24:25AM +0100, Jan Kara wrote:
> On Tue 21-02-17 10:19:28, Jens Axboe wrote:
> > On 02/21/2017 10:09 AM, Jan Kara wrote:
> > > Hello,
> > > 
> > > this is a second revision of the patch set to fix several different races and
> > > issues I've found when testing device shutdown and reuse. The first three
> > > patches are fixes to problems in my previous series fixing BDI lifetime issues.
> > > Patch 4 fixes issues with reuse of BDI name with scsi devices. With it I cannot
> > > reproduce the BDI name reuse issues using Omar's stress test using scsi_debug
> > > so it can be used as a replacement of Dan's patches. Patches 5-11 fix oops that
> > > is triggered by __blkdev_put() calling inode_detach_wb() too early (the problem
> > > reported by Thiago). Patches 12 and 13 fix oops due to a bug in gendisk code
> > > where get_gendisk() can return already freed gendisk structure (again triggered
> > > by Omar's stress test).
> > > 
> > > People, please have a look at patches. They are mostly simple however the
> > > interactions are rather complex so I may have missed something. Also I'm
> > > happy for any additional testing these patches can get - I've stressed them
> > > with Omar's script, tested memcg writeback, tested static (not udev managed)
> > > device inodes.
> > > 
> > > Jens, I think at least patches 1-3 should go in together with my fixes you
> > > already have in your tree (or shortly after them). It is up to you whether
> > > you decide to delay my first fixes or pick these up quickly. Patch 4 is
> > > (IMHO a cleaner) replacement of Dan's patches so consider whether you want
> > > to use it instead of those patches.
> > 
> > I have applied 1-3 to my for-linus branch, which will go in after
> > the initial pull request has been pulled by Linus. Consider fixing up
> > #4 so it applies, I like it.
> 
> OK, attached is patch 4 rebased on top of Linus' tree from today which
> already has linux-block changes pulled in. I've left put_disk_devt() in
> blk_cleanup_queue() to maintain the logic in the original patch (now commit
> 0dba1314d4f8) that request_queue and gendisk each hold one devt reference.
> The bdi_unregister() call that is moved to del_gendisk() by this patch is
> now protected by the gendisk reference instead of the request_queue one
> so it still maintains the property that devt reference protects bdi
> registration-unregistration lifetime (as much as that is not needed anymore
> after this patch).
> 
> I have also updated the comment in the code and the changelog - they were
> somewhat stale after changes to the whole series Tejun suggested.
> 
> 								Honza

Hey, Jan, I just tested this out when I was seeing similar crashes with
sr instead of sd, and this fixed it.

Tested-by: Omar Sandoval <osandov@fb.com>