[34-longterm 064/179] md: check ->hot_remove_disk when removing disk

From: Paul Gortmaker
Date: Mon May 14 2012 - 23:03:58 EST

From: Namhyung Kim <namhyung@xxxxxxxxx>

This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.

commit 01393f3d5836b7d62e925e6f4658a7eb22b83a11 upstream.

Check pers->hot_remove_disk instead of pers->hot_add_disk in slot_store()
during disk removal. The linear personality only has ->hot_add_disk and
no ->hot_remove_disk, so that removing disk in the array resulted to
following kernel bug:

$ sudo mdadm --create /dev/md0 --level=linear --raid-devices=4 /dev/loop[0-3]
$ echo none | sudo tee /sys/block/md0/md/dev-loop2/slot
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [< (null)>] (null)
PGD c9f5d067 PUD 8575a067 PMD 0
Oops: 0010 [#1] SMP
Modules linked in: linear loop bridge stp llc kvm_intel kvm asus_atk0110 sr_mod cdrom sg

Pid: 10450, comm: tee Not tainted 3.0.0-rc1-leonard+ #173 System manufacturer System Product Name/P5G41TD-M PRO
RIP: 0010:[<0000000000000000>] [< (null)>] (null)
RSP: 0018:ffff880085757df0 EFLAGS: 00010282
RAX: ffffffffa00168e0 RBX: ffff8800d1431800 RCX: 000000000000006e
RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff88008543c000
RBP: ffff880085757e48 R08: 0000000000000002 R09: 000000000000000a
R10: 0000000000000000 R11: ffff88008543c2e0 R12: 00000000ffffffff
R13: ffff8800b4641000 R14: 0000000000000005 R15: 0000000000000000
FS: 00007fe8c9e05700(0000) GS:ffff88011fa00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000000 CR3: 00000000b4502000 CR4: 00000000000406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process tee (pid: 10450, threadinfo ffff880085756000, task ffff8800c9f08000)
ffffffff8138496a ffff8800b4641000 ffff88008543c268 0000000000000000
ffff8800b4641000 ffff88008543c000 ffff8800d1431868 ffffffff81a78a90
ffff8800b4641000 ffff88008543c000 ffff8800d1431800 ffff880085757e98
Call Trace:
[<ffffffff8138496a>] ? slot_store+0xaa/0x265
[<ffffffff81384bae>] rdev_attr_store+0x89/0xa8
[<ffffffff8115a96a>] sysfs_write_file+0x108/0x144
[<ffffffff81106b87>] vfs_write+0xb1/0x10d
[<ffffffff8106e6c0>] ? trace_hardirqs_on_caller+0x111/0x135
[<ffffffff81106cac>] sys_write+0x4d/0x77
[<ffffffff814fe702>] system_call_fastpath+0x16/0x1b
Code: Bad RIP value.
RIP [< (null)>] (null)
RSP <ffff880085757df0>
CR2: 0000000000000000
---[ end trace ba5fc64319a826fb ]---

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
drivers/md/md.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f468ec6..1287b03 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2391,7 +2391,7 @@ slot_store(mdk_rdev_t *rdev, const char *buf, size_t len)
if (rdev->raid_disk == -1)
return -EEXIST;
/* personality does all needed checks */
- if (rdev->mddev->pers->hot_add_disk == NULL)
+ if (rdev->mddev->pers->hot_remove_disk == NULL)
return -EINVAL;
err = rdev->mddev->pers->
hot_remove_disk(rdev->mddev, rdev->raid_disk);

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