506a2001b7
[ Upstream commit 2cafe29a8d03f02a3d16193bdaae2f3e82a423f9 ] Yi reported several kernel panics on: [16687.001777] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008 ... [16687.163549] pc : __rq_qos_track+0x38/0x60 or [ 997.690455] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020 ... [ 997.850347] pc : __rq_qos_done+0x2c/0x50 Turns out it is caused by race between adding rq qos(wbt) and normal IO because rq_qos_add can be run when IO is being submitted, fix this issue by freezing queue before adding/deleting rq qos to queue. rq_qos_exit() needn't to freeze queue because it is called after queue has been frozen. iolatency calls rq_qos_add() during allocating queue, so freezing won't add delay because queue usage refcount works at atomic mode at that time. iocost calls rq_qos_add() when writing cgroup attribute file, that is fine to freeze queue at that time since we usually freeze queue when storing to queue sysfs attribute, meantime iocost only exists on the root cgroup. wbt_init calls it in blk_register_queue() and queue sysfs attribute store(queue_wb_lat_store() when write it 1st time in case of !BLK_WBT_MQ), the following patch will speedup the queue freezing in wbt_init. Reported-by: Yi Zhang <yi.zhang@redhat.com> Cc: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Yi Zhang <yi.zhang@redhat.com> Link: https://lore.kernel.org/r/20210609015822.103433-2-ming.lei@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.