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

[Dan Williams]

On Sun, Jan 29, 2017 at 11:22 PM, Omar Sandoval <osandov@xxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxxxxxxxxxx>
>> > Cc: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
>> > Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
>> > Cc: Christoph Hellwig <hch@xxxxxx>
>> > Cc: Jens Axboe <axboe@xxxxxxxxx>
>> > Reported-by: Omar Sandoval <osandov@xxxxxxxxxxx>
>> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>> > ---
>> >  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.

Correct. In fact I was running Jan's patches in my baseline kernel
that fails almost immediately.