From 814d04e7dfc4a9cf7e36656afe2da5c0c08dde2b Mon Sep 17 00:00:00 2001 From: Valentin Priescu Date: Tue, 20 May 2014 22:28:50 +0200 Subject: xen-blkback: defer freeing blkif to avoid blocking xenwatch Currently xenwatch blocks in VBD disconnect, waiting for all pending I/O requests to finish. If the VBD is attached to a hot-swappable disk, then xenwatch can hang for a long period of time, stalling other watches. INFO: task xenwatch:39 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. ffff880057f01bd0 0000000000000246 ffff880057f01ac0 ffffffff810b0782 ffff880057f01ad0 00000000000131c0 0000000000000004 ffff880057edb040 ffff8800344c6080 0000000000000000 ffff880058c00ba0 ffff880057edb040 Call Trace: [] ? irq_to_desc+0x12/0x20 [] ? list_del+0x11/0x40 [] ? wait_for_common+0x60/0x160 [] ? _raw_spin_lock_irqsave+0x2f/0x50 [] ? _raw_spin_unlock_irqrestore+0x19/0x20 [] schedule+0x3a/0x60 [] xen_blkif_disconnect+0x8a/0x100 [xen_blkback] [] ? wake_up_bit+0x40/0x40 [] xen_blkbk_remove+0xae/0x1e0 [xen_blkback] [] xenbus_dev_remove+0x44/0x90 [] __device_release_driver+0x77/0xd0 [] device_release_driver+0x28/0x40 [] bus_remove_device+0x78/0xe0 [] device_del+0x12f/0x1a0 [] device_unregister+0x1d/0x60 [] frontend_changed+0xa6/0x4d0 [xen_blkback] [] ? frontend_changed+0x192/0x650 [xen_netback] [] ? cmp_dev+0x60/0x60 [] ? bus_for_each_dev+0x94/0xa0 [] xenbus_otherend_changed+0xbe/0x120 [] frontend_changed+0xb/0x10 [] xenwatch_thread+0xf2/0x130 [] ? wake_up_bit+0x40/0x40 [] ? xenbus_directory+0x80/0x80 [] kthread+0x96/0xa0 [] kernel_thread_helper+0x4/0x10 [] ? int_ret_from_sys_call+0x7/0x1b [] ? retint_restore_args+0x5/0x6 [] ? gs_change+0x13/0x13 With this patch, when there is still pending I/O, the actual disconnect is done by the last reference holder (last pending I/O request). In this case, xenwatch doesn't block indefinitely. Signed-off-by: Valentin Priescu Reviewed-by: Steven Kady Reviewed-by: Steven Noonan Reviewed-by: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk --- drivers/block/xen-blkback/common.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/block/xen-blkback/common.h') diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index be052773ad03..f65b807e3236 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -314,7 +314,7 @@ struct xen_blkif { unsigned long long st_rd_sect; unsigned long long st_wr_sect; - wait_queue_head_t waiting_to_free; + struct work_struct free_work; /* Thread shutdown wait queue. */ wait_queue_head_t shutdown_wq; }; @@ -361,7 +361,7 @@ struct pending_req { #define xen_blkif_put(_b) \ do { \ if (atomic_dec_and_test(&(_b)->refcnt)) \ - wake_up(&(_b)->waiting_to_free);\ + schedule_work(&(_b)->free_work);\ } while (0) struct phys_req { -- cgit v1.2.3