linux-kernel - Re: [RFC PATCH] scsi, block: fix duplicate bdi name registration crashes

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Date:   Sun, 29 Jan 2017 23:22:59 -0800
From:   Omar Sandoval <osandov@...ndov.com>
To:     Hannes Reinecke <hare@...e.de>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        martin.petersen@...cle.com, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH] scsi, block: fix duplicate bdi name registration
 crashes

On Mon, Jan 30, 2017 at 08:05:52AM +0100, Hannes Reinecke wrote:
> On 01/29/2017 05:58 AM, Dan Williams wrote:
> > Warnings of the following form occur because scsi reuses a devt number
> > while the block layer still has it referenced as the name of the bdi
> > [1]:
> > 
> >  WARNING: CPU: 1 PID: 93 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x62/0x80
> >  sysfs: cannot create duplicate filename '/devices/virtual/bdi/8:192'
> >  [..]
> >  Call Trace:
> >   dump_stack+0x86/0xc3
> >   __warn+0xcb/0xf0
> >   warn_slowpath_fmt+0x5f/0x80
> >   ? kernfs_path_from_node+0x4f/0x60
> >   sysfs_warn_dup+0x62/0x80
> >   sysfs_create_dir_ns+0x77/0x90
> >   kobject_add_internal+0xb2/0x350
> >   kobject_add+0x75/0xd0
> >   device_add+0x15a/0x650
> >   device_create_groups_vargs+0xe0/0xf0
> >   device_create_vargs+0x1c/0x20
> >   bdi_register+0x90/0x240
> >   ? lockdep_init_map+0x57/0x200
> >   bdi_register_owner+0x36/0x60
> >   device_add_disk+0x1bb/0x4e0
> >   ? __pm_runtime_use_autosuspend+0x5c/0x70
> >   sd_probe_async+0x10d/0x1c0
> >   async_run_entry_fn+0x39/0x170
> > 
> > This is a brute-force fix to pass the devt release information from
> > sd_probe() to the locations where we register the bdi,
> > device_add_disk(), and unregister the bdi, blk_cleanup_queue().
> > 
> > Thanks to Omar for the quick reproducer script [2]. This patch survives
> > where an unmodified kernel fails in a few seconds.
> > 
> > [1]: https://marc.info/?l=linux-scsi&m=147116857810716&w=4
> > [2]: http://marc.info/?l=linux-block&m=148554717109098&w=2
> > 
> > Cc: James Bottomley <James.Bottomley@...senpartnership.com>
> > Cc: Bart Van Assche <bart.vanassche@...disk.com>
> > Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Jens Axboe <axboe@...nel.dk>
> > Reported-by: Omar Sandoval <osandov@...ndov.com>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  block/blk-core.c       |    1 +
> >  block/genhd.c          |    7 +++++++
> >  drivers/scsi/sd.c      |   41 +++++++++++++++++++++++++++++++++--------
> >  include/linux/blkdev.h |    1 +
> >  include/linux/genhd.h  |   17 +++++++++++++++++
> >  5 files changed, 59 insertions(+), 8 deletions(-)
> > 
> Please check the patchset from Jan Kara (cf 'BDI lifetime fix' on
> linux-block), which attempts to solve the same problem.

Hi, Hannes,

It's not the same problem. Jan's series fixes a bdi vs. inode lifetime
issue, this patch is for a bdi vs devt lifetime issue. Jan's series
doesn't fix the crashes caused by my reproducer script.