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| author | Dan Williams <dan.j.williams@intel.com> | 2012-04-06 13:41:06 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-04-10 14:48:51 -0700 |
| commit | 3a198886ab5f228fcbebb9ace803d8b99721d49a (patch) | |
| tree | 6f9132521f9d873ce1e3bf38c60d9ea4bdb87405 /fs/sysfs | |
| parent | 5631f2c18f4b2845b3e97df1c659c5094a17605f (diff) | |
| download | lwn-3a198886ab5f228fcbebb9ace803d8b99721d49a.tar.gz lwn-3a198886ab5f228fcbebb9ace803d8b99721d49a.zip | |
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>
Diffstat (limited to 'fs/sysfs')
| -rw-r--r-- | fs/sysfs/dir.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index 8ddc1021c79a..35a36d39fa2c 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -729,6 +729,9 @@ int sysfs_create_dir(struct kobject * kobj) else parent_sd = &sysfs_root; + if (!parent_sd) + return -ENOENT; + if (sysfs_ns_type(parent_sd)) ns = kobj->ktype->namespace(kobj); type = sysfs_read_ns_type(kobj); |