linux/fs/sysfs
Dan Williams 3a198886ab sysfs: handle 'parent deleted before child added'
In scsi at least two cases of the parent device being deleted before the
child is added have been observed.

1/ scsi is performing async scans and the device is removed prior to the
   async can thread running (can happen with an in-opportune / unlikely
   unplug during initial scan).

2/ libsas discovery event running after the parent port has been torn
   down (this is a bug in libsas).

Result in crash signatures like:
 BUG: unable to handle kernel NULL pointer dereference at 0000000000000098
 IP: [<ffffffff8115e100>] sysfs_create_dir+0x32/0xb6
 ...
 Process scsi_scan_8 (pid: 5417, threadinfo ffff88080bd16000, task ffff880801b8a0b0)
 Stack:
  00000000fffffffe ffff880813470628 ffff88080bd17cd0 ffff88080614b7e8
  ffff88080b45c108 00000000fffffffe ffff88080bd17d20 ffffffff8125e4a8
  ffff88080bd17cf0 ffffffff81075149 ffff88080bd17d30 ffff88080614b7e8
 Call Trace:
  [<ffffffff8125e4a8>] kobject_add_internal+0x120/0x1e3
  [<ffffffff81075149>] ? trace_hardirqs_on+0xd/0xf
  [<ffffffff8125e641>] kobject_add_varg+0x41/0x50
  [<ffffffff8125e70b>] kobject_add+0x64/0x66
  [<ffffffff8131122b>] device_add+0x12d/0x63a

In this scenario the parent is still valid (because we have a
reference), but it has been device_del()'d which means its kobj->sd
pointer is NULL'd via:

 device_del()->kobject_del()->sysfs_remove_dir()

...and then sysfs_create_dir() (without this fix) goes ahead and
de-references parent_sd via sysfs_ns_type():

 return (sd->s_flags & SYSFS_NS_TYPE_MASK) >> SYSFS_NS_TYPE_SHIFT;

This scenario is being fixed in scsi/libsas, but if other subsystems
present the same ordering the system need not immediately crash.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: James Bottomley <JBottomley@parallels.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2012-04-10 14:48:51 -07:00
..
bin.c sysfs: only access bin file vm_ops with the active lock 2010-10-22 10:16:43 -07:00
dir.c sysfs: handle 'parent deleted before child added' 2012-04-10 14:48:51 -07:00
file.c sysfs: Complain bitterly about attempts to remove files from nonexistent directories. 2012-01-24 12:12:32 -08:00
group.c sysfs: Prevent crash on unset sysfs group attributes 2012-04-10 14:48:51 -07:00
inode.c Revert "sysfs: Kill nlink counting." 2012-03-08 13:03:10 -08:00
Kconfig kconfig: rename CONFIG_EMBEDDED to CONFIG_EXPERT 2011-01-20 17:02:05 -08:00
Makefile Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mount.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
symlink.c sysfs: allow creating symlinks from untagged to tagged directories 2010-07-26 12:02:41 -07:00
sysfs.h Revert "sysfs: Kill nlink counting." 2012-03-08 13:03:10 -08:00