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Date: Thu, 2 Jun 2011 15:53:15 +1000
From: NeilBrown <neilb@suse.de>
To: Namhyung Kim <namhyung@gmail.com>
Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@kernel.org
Subject: Re: [PATCH 2/2] md: check ->hot_remove_disk when removing disk
Message-ID: <20110602155315.31b01a23@notabene.brown>
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On Thu,  2 Jun 2011 13:53:03 +0900 Namhyung Kim <namhyung@gmail.com> wrote:

> 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
>  CPU 2
>  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)
>  Stack:
>   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@gmail.com>
> Cc: stable@kernel.org
> ---
>  drivers/md/md.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index f210e42a56ca..3db106b7b245 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -2461,7 +2461,7 @@ 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);

Thanks.  I've applied this to my tree and will push it to Linus in due
course.

NeilBrown
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