[Xen-devel] xl hangs instead of failing more graciously when the fs is read-only

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Hi Ian,

At the moment Iâm having the privilege of thrashing my box and root-fs 
frequently while testing kernels. This causes the root-fs to be mounted 
read-only. But init continues to do it's job any way .. so we get to xendomains,
which in turn uses 'xl'. But 'xl' needs a writable FS and hangs when it's not,
couldn't and shouldn't this fail more graciously ?

--
Sander
 
[  374.387283] INFO: task xl:9233 blocked for more than 120 seconds.
[  374.401747]       Not tainted 3.15.0-20140611a-netnext+ #1
[  374.416089] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this 
message.
[  374.428468] xl              D ffff880033a80000     0  9233   9231 0x00000000
[  374.439931]  ffff88002a617d78 0000000000000216 ffff880033a80000 
0000000000014500
[  374.451387]  ffff88002a617fd8 0000000000014500 ffffffff822184e0 
ffff880033a80000
[  374.462742]  000000101c8101e6 ffffffff8313deb0 ffff880033a80000 
ffff880033a80850
[  374.474082] Call Trace:
[  374.485344]  [<ffffffff81116426>] ? __lock_acquire+0x516/0x2210
[  374.496464]  [<ffffffff8111448a>] ? mark_held_locks+0x6a/0x90
[  374.507358]  [<ffffffff81ba9239>] schedule+0x29/0x70
[  374.518145]  [<ffffffff81ba964e>] schedule_preempt_disabled+0xe/0x10
[  374.528861]  [<ffffffff81bac86a>] mutex_lock_nested+0x17a/0x560
[  374.539422]  [<ffffffff81590267>] ? xenbus_dev_request_and_reply+0x37/0xc0
[  374.550001]  [<ffffffff81590267>] xenbus_dev_request_and_reply+0x37/0xc0
[  374.560543]  [<ffffffff811be2f3>] ? might_fault+0x43/0xa0
[  374.570927]  [<ffffffff815921e8>] xenbus_file_write+0x2c8/0x560
[  374.581130]  [<ffffffff8111856c>] ? lock_release+0x13c/0x2a0
[  374.591086]  [<ffffffff811f71e2>] vfs_write+0xc2/0x1e0
[  374.600943]  [<ffffffff811f76f2>] SyS_write+0x52/0xc0
[  374.610673]  [<ffffffff81baf939>] system_call_fastpath+0x16/0x1b
[  374.620293] 3 locks held by xl/9233:
[  374.629816]  #0:  (sb_writers#10){.+.+..}, at: [<ffffffff811f72e3>] 
vfs_write+0x1c3/0x1e0
[  374.639444]  #1:  (&u->msgbuffer_mutex){+.+...}, at: [<ffffffff81591f6a>] 
xenbus_file_write+0x4a/0x560
[  374.649015]  #2:  (&xs_state.request_mutex){+.+...}, at: 
[<ffffffff81590267>] xenbus_dev_request_and_reply+0x37/0xc0
[  494.597619] INFO: task xl:9233 blocked for more than 120 seconds.
[  494.609487]       Not tainted 3.15.0-20140611a-netnext+ #1
[  494.621051] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this 
message.
[  494.630382] xl              D ffff880033a80000     0  9233   9231 0x00000000
[  494.639750]  ffff88002a617d78 0000000000000216 ffff880033a80000 
0000000000014500
[  494.649113]  ffff88002a617fd8 0000000000014500 ffffffff822184e0 
ffff880033a80000
[  494.658231]  000000101c8101e6 ffffffff8313deb0 ffff880033a80000 
ffff880033a80850
[  494.667179] Call Trace:
[  494.675972]  [<ffffffff81116426>] ? __lock_acquire+0x516/0x2210
[  494.684793]  [<ffffffff8111448a>] ? mark_held_locks+0x6a/0x90
[  494.693479]  [<ffffffff81ba9239>] schedule+0x29/0x70
[  494.702161]  [<ffffffff81ba964e>] schedule_preempt_disabled+0xe/0x10
[  494.710782]  [<ffffffff81bac86a>] mutex_lock_nested+0x17a/0x560
[  494.719166]  [<ffffffff81590267>] ? xenbus_dev_request_and_reply+0x37/0xc0
[  494.727404]  [<ffffffff81590267>] xenbus_dev_request_and_reply+0x37/0xc0
[  494.735528]  [<ffffffff811be2f3>] ? might_fault+0x43/0xa0
[  494.743583]  [<ffffffff815921e8>] xenbus_file_write+0x2c8/0x560
[  494.751505]  [<ffffffff8111856c>] ? lock_release+0x13c/0x2a0
[  494.759406]  [<ffffffff811f71e2>] vfs_write+0xc2/0x1e0
[  494.767192]  [<ffffffff811f76f2>] SyS_write+0x52/0xc0
[  494.774714]  [<ffffffff81baf939>] system_call_fastpath+0x16/0x1b
[  494.782034] 3 locks held by xl/9233:
[  494.789223]  #0:  (sb_writers#10){.+.+..}, at: [<ffffffff811f72e3>] 
vfs_write+0x1c3/0x1e0
[  494.796547]  #1:  (&u->msgbuffer_mutex){+.+...}, at: [<ffffffff81591f6a>] 
xenbus_file_write+0x4a/0x560
[  494.803955]  #2:  (&xs_state.request_mutex){+.+...}, at: 
[<ffffffff81590267>] xenbus_dev_request_and_reply+0x37/0xc0


etc. etc.

  



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