[libsas PATCH v12 04/11] sysfs: handle 'parent deleted before child added'

[Dan Williams <dan.j.williams@intel.com>]

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.

2/ libsas discovery event running after the parent port has been torn
   down.

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

These scenarios need to be cleaned up, but in the meantime the system
need not crash if this ordering occurs.  Instead report:

 kobject_add_internal failed for target8:0:16 (error: -2 parent: end_device-8:0:24)
 Pid: 2942, comm: scsi_scan_8 Not tainted 3.3.0-rc7-isci+ #2
 Call Trace:
  [<ffffffff8125e551>] kobject_add_internal+0x1c1/0x1f3
  [<ffffffff81075149>] ? trace_hardirqs_on+0xd/0xf
  [<ffffffff8125e659>] kobject_add_varg+0x41/0x50
  [<ffffffff8125e723>] kobject_add+0x64/0x66
  [<ffffffff8131124b>] device_add+0x12d/0x63a
  [<ffffffff8125e0ef>] ? kobject_put+0x4c/0x50
  [<ffffffff8132f370>] scsi_sysfs_add_sdev+0x4e/0x28a
  [<ffffffff8132dce3>] do_scan_async+0x9c/0x145

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/sysfs/dir.c |    3 +++
 lib/kobject.c  |    7 ++++---
 2 files changed, 7 insertions(+), 3 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);
diff --git a/lib/kobject.c b/lib/kobject.c
index c33d7a1..e5f86c0 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -192,13 +192,14 @@ static int kobject_add_internal(struct kobject *kobj)
 
 		/* be noisy on error issues */
 		if (error == -EEXIST)
-			printk(KERN_ERR "%s failed for %s with "
+			pr_err("%s failed for %s with "
 			       "-EEXIST, don't try to register things with "
 			       "the same name in the same directory.\n",
 			       __func__, kobject_name(kobj));
 		else
-			printk(KERN_ERR "%s failed for %s (%d)\n",
-			       __func__, kobject_name(kobj), error);
+			pr_err("%s failed for %s (error: %d parent: %s)\n",
+			       __func__, kobject_name(kobj), error,
+			       parent ? kobject_name(parent) : "'none'");
 		dump_stack();
 	} else
 		kobj->state_in_sysfs = 1;