Re: [Xen-devel] [PATCH] Fix blkback/blktap sysfs read bug.

["Joe Jin" <joe.jin@xxxxxxxxxx>]

> Your patch will work okay on 2.6.18.
> 
> But collisions will deadlock after 2.6.23
> 
> Found an old stack trace:
> 
> [2009-07-08 06:15:08 UTC] INFO: task xb.00021.xvdd:30039 blocked for more 
> than 120 seconds.
> [2009-07-08 06:15:08 UTC] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" 
> disables this message.
> [2009-07-08 06:15:08 UTC]        c7adfe0c 00000246 00000000 00000000 5b88fd4f 
> 00000256 c7ade000 c7adfdc8 
> [2009-07-08 06:15:08 UTC]        c0107c1b 38c984a4 00000256 c7adfddc ed629578 
> ed6293f0 ed629578 c16bdb00 
> [2009-07-08 06:15:08 UTC]        00000000 eea0d500 c16bdb34 002dc05a 00000000 
> 00000005 0024c31c e20a8ff0 
> [2009-07-08 06:15:08 UTC] Call Trace:
> [2009-07-08 06:15:08 UTC]  [<c0107c1b>] ? local_clock+0x3b/0x90
> [2009-07-08 06:15:08 UTC]  [<c0344675>] schedule_timeout+0x75/0xc0
> [2009-07-08 06:15:08 UTC]  [<c011ed81>] ? pick_next_task_fair+0x91/0xd0
> [2009-07-08 06:15:08 UTC]  [<c03442c9>] wait_for_common+0xa9/0x1c0
> [2009-07-08 06:15:08 UTC]  [<c0120d40>] ? default_wake_function+0x0/0x10
> [2009-07-08 06:15:08 UTC]  [<c0344472>] wait_for_completion+0x12/0x20
> [2009-07-08 06:15:08 UTC]  [<c01cf9e7>] sysfs_addrm_finish+0x1e7/0x230
> [2009-07-08 06:15:08 UTC]  [<c01ce2e5>] sysfs_hash_and_remove+0x45/0x70
> [2009-07-08 06:15:08 UTC]  [<c01d0adb>] remove_files+0x1b/0x30
> [2009-07-08 06:15:08 UTC]  [<c01d0b26>] sysfs_remove_group+0x36/0xc0
> [2009-07-08 06:15:08 UTC]  [<c01ae02f>] ? __blkdev_put+0x14f/0x160
> [2009-07-08 06:15:08 UTC]  [<c02769fc>] xenvbd_sysfs_delif+0x2c/0x60
> [2009-07-08 06:15:08 UTC]  [<c0276a76>] blkback_close+0x46/0x70
> [2009-07-08 06:15:08 UTC]  [<c0275d33>] blkif_schedule+0x583/0x5b0
> [2009-07-08 06:15:08 UTC]  [<c011ed81>] ? pick_next_task_fair+0x91/0xd0
> [2009-07-08 06:15:08 UTC]  [<c013dda0>] ? autoremove_wake_function+0x0/0x50
> [2009-07-08 06:15:08 UTC]  [<c02757b0>] ? blkif_schedule+0x0/0x5b0
> [2009-07-08 06:15:08 UTC]  [<c013da42>] kthread+0x42/0x70
> [2009-07-08 06:15:08 UTC]  [<c013da00>] ? kthread+0x0/0x70
> [2009-07-08 06:15:08 UTC]  [<c010561b>] kernel_thread_helper+0x7/0x10
> 
> The reason is in sysfs_deactivate(), which will sync callers against any
> remaining thread in .show()
> - show() hangs on the lock
> - the lock holder in sysfs_remove_group(), 
>   waiting for show() to complete.
> 
> Pardon me -- I'm not entirely sure where/how these patches are currently
> submitted and merged. I suppose yours are only for linux-2.6.18.hg, not
> e.g. pvops? Then sorry for any confusion.
> 

Daniel, 

Thanks a lot of your comments, it really help for me, yes my patch based 
linux-2.6.18.hg branch. As Jan have pointed out in previous email, it should 
be sysfs's issue, looked like later kernel sysfs have fixed the issue?

Thanks,
Joe


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