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@xxxxxxxxxxxxxxxxxxx> Cc: James Bottomley <JBottomley@xxxxxxxxxxxxx> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> --- Changes since v1: http://marc.info/?l=linux-scsi&m=133239707303441&w=2 1/ split out the kobject_add_internal() warning message changes into its own patch 2/ clarified the changelog a bit due to the discussion from v1. I think this patch can wait until 3.5, since it is just closing a hole I found along the way to fixing the real bug. Now, the system won't crash at device_add() time, but the system may still be de-stabilized if the caller does not handle device_add() errors properly. 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 7fdf6a7..86521ee 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -714,6 +714,9 @@ 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); -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
