f25191bb32
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. Signed-off-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.