Fix a recently introduced deadlock #371
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Some but not all .ra_pages changes happen while block layer I/O is paused with blk_mq_freeze_queue(). Filesystems may read .ra_pages even while block layer I/O is paused, e.g. from inside their .fadvise callback. Annotating all .ra_pages reads with READ_ONCE() would be cumbersome. Hence, add the __data_racy annotatation to the .ra_pages member variable. Cc: Alexander Viro <[email protected]> Cc: Christian Brauner <[email protected]> Cc: Nilay Shroff <[email protected]> Signed-off-by: Bart Van Assche <[email protected]> Reviewed-by: Nilay Shroff <[email protected]>
Freezing the request queue from inside sysfs store callbacks may cause a deadlock in combination with the dm-multipath driver and the queue_if_no_path option. Additionally, freezing the request queue slows down system boot on systems where sysfs attributes are set synchronously. Fix this by removing the blk_mq_freeze_queue() / blk_mq_unfreeze_queue() calls from the store callbacks that do not strictly need these callbacks. Add the __data_racy annotation to request_queue.rq_timeout to suppress KCSAN data race reports about the rq_timeout reads. This patch may cause a small delay in applying the new settings. For all the attributes affected by this patch, I/O will complete correctly whether the old or the new value of the attribute is used. This patch affects the following sysfs attributes: * io_poll_delay * io_timeout * nomerges * read_ahead_kb * rq_affinity Here is an example of a deadlock triggered by running test srp/002 if this patch is not applied: task:multipathd Call Trace: <TASK> __schedule+0x8c1/0x1bf0 schedule+0xdd/0x270 schedule_preempt_disabled+0x1c/0x30 __mutex_lock+0xb89/0x1650 mutex_lock_nested+0x1f/0x30 dm_table_set_restrictions+0x823/0xdf0 __bind+0x166/0x590 dm_swap_table+0x2a7/0x490 do_resume+0x1b1/0x610 dev_suspend+0x55/0x1a0 ctl_ioctl+0x3a5/0x7e0 dm_ctl_ioctl+0x12/0x20 __x64_sys_ioctl+0x127/0x1a0 x64_sys_call+0xe2b/0x17d0 do_syscall_64+0x96/0x3a0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK> task:(udev-worker) Call Trace: <TASK> __schedule+0x8c1/0x1bf0 schedule+0xdd/0x270 blk_mq_freeze_queue_wait+0xf2/0x140 blk_mq_freeze_queue_nomemsave+0x23/0x30 queue_ra_store+0x14e/0x290 queue_attr_store+0x23e/0x2c0 sysfs_kf_write+0xde/0x140 kernfs_fop_write_iter+0x3b2/0x630 vfs_write+0x4fd/0x1390 ksys_write+0xfd/0x230 __x64_sys_write+0x76/0xc0 x64_sys_call+0x276/0x17d0 do_syscall_64+0x96/0x3a0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK> Cc: Christoph Hellwig <[email protected]> Cc: Ming Lei <[email protected]> Cc: Nilay Shroff <[email protected]> Cc: Martin Wilck <[email protected]> Cc: Benjamin Marzinski <[email protected]> Cc: [email protected] Fixes: af28141 ("block: freeze the queue in queue_attr_store") Signed-off-by: Bart Van Assche <[email protected]> Reviewed-by: Nilay Shroff <[email protected]>
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Pull request for series with
subject: Fix a recently introduced deadlock
version: 6
url: https://patchwork.kernel.org/project/linux-block/list/?series=1023735