Re: [PATCH] UBI: block: Fix locking for idr_alloc/idr_remove

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jan 18, 2018 at 08:47:41AM -0500, Bradley Bolen wrote:
> From: Bradley Bolen <bradleybolen@gmail.com>
> 
> This fixes a race with idr_alloc where gd->first_minor can be set to the
> same value for two simultaneous calls to ubiblock_create.  Each instance
> calls device_add_disk with the same first_minor.  device_add_disk calls
> bdi_register_owner which generates several warnings.
> 
> WARNING: CPU: 1 PID: 179 at kernel-source/fs/sysfs/dir.c:31
> sysfs_warn_dup+0x68/0x88
> sysfs: cannot create duplicate filename '/devices/virtual/bdi/252:2'
> 
> WARNING: CPU: 1 PID: 179 at kernel-source/lib/kobject.c:240
> kobject_add_internal+0x1ec/0x2f8
> kobject_add_internal failed for 252:2 with -EEXIST, don't try to
> register things with the same name in the same directory
> 
> WARNING: CPU: 1 PID: 179 at kernel-source/fs/sysfs/dir.c:31
> sysfs_warn_dup+0x68/0x88
> sysfs: cannot create duplicate filename '/dev/block/252:2'
> 
> However, device_add_disk does not error out when bdi_register_owner
> returns an error.  Control continues until reaching blk_register_queue.
> It then BUGs.
> 
> kernel BUG at kernel-source/fs/sysfs/group.c:113!
> [<c01e26cc>] (internal_create_group) from [<c01e2950>]
> (sysfs_create_group+0x20/0x24)
> [<c01e2950>] (sysfs_create_group) from [<c00e3d38>]
> (blk_trace_init_sysfs+0x18/0x20)
> [<c00e3d38>] (blk_trace_init_sysfs) from [<c02bdfbc>]
> (blk_register_queue+0xd8/0x154)
> [<c02bdfbc>] (blk_register_queue) from [<c02cec84>]
> (device_add_disk+0x194/0x44c)
> [<c02cec84>] (device_add_disk) from [<c0436ec8>]
> (ubiblock_create+0x284/0x2e0)
> [<c0436ec8>] (ubiblock_create) from [<c0427bb8>]
> (vol_cdev_ioctl+0x450/0x554)
> [<c0427bb8>] (vol_cdev_ioctl) from [<c0189110>] (vfs_ioctl+0x30/0x44)
> [<c0189110>] (vfs_ioctl) from [<c01892e0>] (do_vfs_ioctl+0xa0/0x790)
> [<c01892e0>] (do_vfs_ioctl) from [<c0189a14>] (SyS_ioctl+0x44/0x68)
> [<c0189a14>] (SyS_ioctl) from [<c0010640>] (ret_fast_syscall+0x0/0x34)
> 
> Locking idr_alloc/idr_remove removes the race and keeps gd->first_minor
> unique.
> 
> Fixes: 2bf50d42f3a4 ("UBI: block: Dynamically allocate minor numbers")
> Cc: stable@vger.kernel.org
> Signed-off-by: Bradley Bolen <bradleybolen@gmail.com>
> ---
>  drivers/mtd/ubi/block.c | 42 ++++++++++++++++++++++++++----------------
>  1 file changed, 26 insertions(+), 16 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

It's also not how you submit patches upstream, you have read
Documentation/SubmittingPatches, right?

thanks,

greg k-h