lkml.org 
[lkml]   [2019]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] cdrom: Fix race condition in cdrom_sysctl_register
From
Date
On 2/6/19 10:13 PM, Guenter Roeck wrote:
> The following traceback is sometimes seen when booting an image in qemu:
>
> [ 54.608293] cdrom: Uniform CD-ROM driver Revision: 3.20
> [ 54.611085] Fusion MPT base driver 3.04.20
> [ 54.611877] Copyright (c) 1999-2008 LSI Corporation
> [ 54.616234] Fusion MPT SAS Host driver 3.04.20
> [ 54.635139] sysctl duplicate entry: /dev/cdrom//info
> [ 54.639578] CPU: 0 PID: 266 Comm: kworker/u4:5 Not tainted 5.0.0-rc5 #1
> [ 54.639578] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> [ 54.641273] Workqueue: events_unbound async_run_entry_fn
> [ 54.641273] Call Trace:
> [ 54.641273] dump_stack+0x67/0x90
> [ 54.641273] __register_sysctl_table+0x50b/0x570
> [ 54.641273] ? rcu_read_lock_sched_held+0x6f/0x80
> [ 54.641273] ? kmem_cache_alloc_trace+0x1c7/0x1f0
> [ 54.646814] __register_sysctl_paths+0x1c8/0x1f0
> [ 54.646814] cdrom_sysctl_register.part.7+0xc/0x5f
> [ 54.646814] register_cdrom.cold.24+0x2a/0x33
> [ 54.646814] sr_probe+0x4bd/0x580
> [ 54.646814] ? __driver_attach+0xd0/0xd0
> [ 54.646814] really_probe+0xd6/0x260
> [ 54.646814] ? __driver_attach+0xd0/0xd0
> [ 54.646814] driver_probe_device+0x4a/0xb0
> [ 54.646814] ? __driver_attach+0xd0/0xd0
> [ 54.646814] bus_for_each_drv+0x73/0xc0
> [ 54.646814] __device_attach+0xd6/0x130
> [ 54.646814] bus_probe_device+0x9a/0xb0
> [ 54.646814] device_add+0x40c/0x670
> [ 54.646814] ? __pm_runtime_resume+0x4f/0x80
> [ 54.646814] scsi_sysfs_add_sdev+0x81/0x290
> [ 54.646814] scsi_probe_and_add_lun+0x888/0xc00
> [ 54.646814] ? scsi_autopm_get_host+0x21/0x40
> [ 54.646814] __scsi_add_device+0x116/0x130
> [ 54.646814] ata_scsi_scan_host+0x93/0x1c0
> [ 54.646814] async_run_entry_fn+0x34/0x100
> [ 54.646814] process_one_work+0x237/0x5e0
> [ 54.646814] worker_thread+0x37/0x380
> [ 54.646814] ? rescuer_thread+0x360/0x360
> [ 54.646814] kthread+0x118/0x130
> [ 54.646814] ? kthread_create_on_node+0x60/0x60
> [ 54.646814] ret_from_fork+0x3a/0x50
>
> The only sensible explanation is that cdrom_sysctl_register() is called
> twice, once from the module init function and once from register_cdrom().
> cdrom_sysctl_register() is not mutex protected and may happily execute
> twice if the second call is made before the first call is complete.
>
> Use a static atomic to ensure that the function is executed exactly once.

Applied, thanks.

--
Jens Axboe

\
 
 \ /
  Last update: 2019-02-08 14:47    [W:0.044 / U:1.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site