Re: [PATCH RESEND v4 0/4] device_list_add() peparation to add reappearing missing device

[Anand Jain <anand.jain@oracle.com>]

On 01/20/2018 07:27 AM, David Sterba wrote:
> On Thu, Jan 18, 2018 at 06:47:17PM +0100, David Sterba wrote:
>> On Thu, Jan 18, 2018 at 10:02:32PM +0800, Anand Jain wrote:
>>> (Apply on top of my patchset
>>>     [PATCH v4 0/6] preparatory work to add device forget
>>>   for conflict free apply. They don't actually depend on
>>>   each other though).
>>
>>> Cleanup of device_list_add(), mainly in preparation to handle
>>> reappearing missing device which its next reroll will be sent
>>> separately.
>>
>> I'm adding the two patchsets to the 4.16 queue but will push the updated
>> branch after the current tests finish and I also test the updated branch
>> as well.
> 
> So this did not survive the first fstests run, I'm going to move the patchset
> to the 4.17 dev queue.
> 
> [ 2912.493351] run fstests btrfs/064 at 2018-01-19 20:55:50
> [ 2914.218654] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 1 transid 5 /dev/sdb6
> [ 2914.261560] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 2 transid 5 /dev/sdc5
> [ 2914.296819] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 3 transid 5 /dev/sdb7
> [ 2914.348140] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 4 transid 5 /dev/sdc6
> [ 2914.389368] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 5 transid 5 /dev/sdb8
> [ 2914.425378] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 6 transid 5 /dev/sdc7
> [ 2914.443497] BTRFS: device fsid ee7e811a-fdb3-42e9-8a81-5ed8e1a4282b devid 7 transid 5 /dev/sdb9
> [ 2914.488145] BTRFS info (device sdb9): disk space caching is enabled
> [ 2914.494744] BTRFS info (device sdb9): has skinny extents
> [ 2914.500328] BTRFS info (device sdb9): flagging fs with big metadata feature
> [ 2914.514809] BTRFS info (device sdb9): enabling ssd optimizations
> [ 2914.522114] BTRFS info (device sdb9): creating UUID tree
> [ 2914.716867] BTRFS info (device sdb9): dev_replace from /dev/sdc5 (devid 2) to /dev/sdc8 started
> [ 2914.852699] BTRFS info (device sdb9): dev_replace from /dev/sdc5 (devid 2) to /dev/sdc8 finished
> [ 2915.028666] BTRFS info (device sdb9): dev_replace from /dev/sdb7 (devid 3) to /dev/sdc5 started
> [ 2915.110374] BTRFS info (device sdb9): dev_replace from /dev/sdb7 (devid 3) to /dev/sdc5 finished
> [ 2915.309674] BTRFS info (device sdb9): dev_replace from /dev/sdc6 (devid 4) to /dev/sdb7 started
> [ 2915.340819] BTRFS info (device sdb9): dev_replace from /dev/sdc6 (devid 4) to /dev/sdb7 finished
> [ 2915.350220] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
> [ 2915.358350] IP: btrfs_scan_one_device+0x127/0x180 [btrfs]
> [ 2915.358353] PGD 0 P4D 0
> [ 2915.358366] Oops: 0000 [#1] PREEMPT SMP
> [ 2915.358493] CPU: 2 PID: 1076 Comm: systemd-udevd Tainted: G        W        4.15.0-rc8-1.ge195904-vanilla+ #128
> [ 2915.358495] Hardware name: empty empty/S3993, BIOS PAQEX0-3 02/24/2008
> [ 2915.358534] RIP: 0010:btrfs_scan_one_device+0x127/0x180 [btrfs]

  I couldn't reproduce with btrfs/064 which ran for several iterations.
  But a script [1] could trigger the problem.

  [1]
---
  mkfs.btrfs -fq -draid1 -mraid1 /dev/sdb /dev/sdc
  modprobe -r btrfs
  mount -o degraded /dev/sdb /btrfs
  btrfs repl start -Bf 2 /dev/sdd /btrfs
  umount /btrfs
  modprobe -r btrfs
  btrfs dev scan
  btrfs dev scan /dev/sdc
---

  Problem was mainly due to the patch 3/4, which tried to access the
  return pointer even for the failed condition. The fix is to bring the
  device point access under the else part as show below [2]. I have
  included this fix in V5. Which is tested with btrfs xfstests.
  Pls could you consider v5 for 4.16 ?

[2]
-----
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 462bae3627e3..a86c3a14ec89 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1214,8 +1214,8 @@ int btrfs_scan_one_device(const char *path, 
fmode_t flags, void *holder,
         mutex_unlock(&uuid_mutex);
         if (IS_ERR(device))
                 ret = PTR_ERR(device);
-
-       *fs_devices_ret = device->fs_devices;
+       else
+               *fs_devices_ret = device->fs_devices;

         btrfs_release_disk_super(page);
------


Thanks, Anand

> [ 2915.358537] RSP: 0018:ffffb35a4524be30 EFLAGS: 00010206
> [ 2915.358541] RAX: fffffffffffffff0 RBX: 0000000000000081 RCX: 000000000000000f
> [ 2915.358544] RDX: ffff96a791c7e10b RSI: 0000000000000001 RDI: ffff96a79f734200
> [ 2915.358546] RBP: ffff96a7a2ea6000 R08: 000000000000002b R09: 0000000000000000
> [ 2915.358548] R10: 0000000000000000 R11: 0000000000000004 R12: 00000000fffffff0
> [ 2915.358550] R13: ffffb35a4524be60 R14: fffff07d48471f80 R15: 000055ee5775ad74
> [ 2915.358554] FS:  00007f736b3648c0(0000) GS:ffff96a7a6a00000(0000) knlGS:0000000000000000
> [ 2915.358556] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 2915.358558] CR2: 0000000000000010 CR3: 000000021201e000 CR4: 00000000000006e0
> [ 2915.358560] Call Trace:
> [ 2915.358600]  btrfs_control_ioctl+0xad/0xe0 [btrfs]
> [ 2915.358610]  ? trace_hardirqs_on_caller+0xf2/0x1a0
> [ 2915.358618]  do_vfs_ioctl+0x90/0x6b0
> [ 2915.358625]  ? __audit_syscall_entry+0xb5/0x110
> [ 2915.358632]  ? syscall_trace_enter+0x1ae/0x360
> [ 2915.358638]  ? return_from_SYSCALL_64+0x10/0x75
> [ 2915.358643]  SyS_ioctl+0x74/0x80
> [ 2915.358647]  ? do_syscall_64+0x1e/0x1a0
> [ 2915.358653]  do_syscall_64+0x64/0x1a0
> [ 2915.358659]  entry_SYSCALL64_slow_path+0x25/0x25
> [ 2915.358663] RIP: 0033:0x7f736a1f3227
> [ 2915.358665] RSP: 002b:00007fff9dcad618 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> [ 2915.358669] RAX: ffffffffffffffda RBX: 00007fff9dcad630 RCX: 00007f736a1f3227
> [ 2915.358670] RDX: 00007fff9dcad630 RSI: 0000000090009427 RDI: 000000000000000f
> [ 2915.358672] RBP: 000000000000000f R08: 376264732f766564 R09: 0000000000000003
> [ 2915.358674] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> [ 2915.358676] R13: 000055ee59813e90 R14: 0000000000000000 R15: 000055ee5775ad74
> [ 2915.358810] RIP: btrfs_scan_one_device+0x127/0x180 [btrfs] RSP: ffffb35a4524be30
> [ 2915.358812] CR2: 0000000000000010
> [ 2915.358970] ---[ end trace 900a4fff1ad9ece2 ]---
> [ 2915.441581] BTRFS info (device sdb9): dev_replace from /dev/sdb8 (devid 5) to /dev/sdc6 started



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