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With preemption enabled (CONFIG_DEBUG_PREEMPT=y), the following appeared when rnbd client tries to map remote block device. BUG: using smp_processor_id() in preemptible [00000000] code: bash/1733 caller is debug_smp_processor_id+0x17/0x20 CPU: 0 PID: 1733 Comm: bash Not tainted 5.16.0-rc1 #5 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x5d/0x78 dump_stack+0x10/0x12 check_preemption_disabled+0xe4/0xf0 debug_smp_processor_id+0x17/0x20 rtrs_clt_update_all_stats+0x3b/0x70 [rtrs_client] rtrs_clt_read_req+0xc3/0x380 [rtrs_client] ? rtrs_clt_init_req+0xe3/0x120 [rtrs_client] rtrs_clt_request+0x1a7/0x320 [rtrs_client] ? 0xffffffffc0ab1000 send_usr_msg+0xbf/0x160 [rnbd_client] ? rnbd_clt_put_sess+0x60/0x60 [rnbd_client] ? send_usr_msg+0x160/0x160 [rnbd_client] ? sg_alloc_table+0x27/0xb0 ? sg_zero_buffer+0xd0/0xd0 send_msg_sess_info+0xe9/0x180 [rnbd_client] ? rnbd_clt_put_sess+0x60/0x60 [rnbd_client] ? blk_mq_alloc_tag_set+0x2ef/0x370 rnbd_clt_map_device+0xba8/0xcd0 [rnbd_client] ? send_msg_open+0x200/0x200 [rnbd_client] rnbd_clt_map_device_store+0x3e5/0x620 [rnbd_client To supress the calltrace, let's call get_cpu_ptr/put_cpu_ptr pair in rtrs_clt_update_rdma_stats to disable preemption when accessing per-cpu variable. While at it, let's make the similar change in rtrs_clt_update_wc_stats. And for rtrs_clt_inc_failover_cnt, though it was only called inside rcu section, but it still can be preempted in case CONFIG_PREEMPT_RCU is enabled, so change it to {get,put}_cpu_ptr pair either. Link: https://lore.kernel.org/r/20211128133501.38710-1-guoqing.jiang@linux.dev Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev> Reviewed-by: Leon Romanovsky <leonro@nvidia.com> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
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.