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Currently while resolving IP address to MAC address single delayed work is used for resolving multiple such resolve requests. This singled work is essentially performs two tasks. (a) any retry needed to resolve and (b) it executes the callback function for all completed requests While work is executing callbacks, any new work scheduled on for this workqueue is lost because workqueue has completed looking at all pending requests and now looking at callbacks, but work is still under execution. Any further retry to look at pending requests in process_req() after executing callbacks would lead to similar race condition (may be reduce the probably further but doesn't eliminate it). Retrying to enqueue work that from queue_req() context is not something rest of the kernel modules have followed. Therefore fix in this patch utilizes kernel facility to enqueue multiple work items to a workqueue. This ensures that no such requests gets lost in synchronization. Request list is still maintained so that rdma_cancel_addr() can unlink the request and get the completion with error sooner. Neighbour update event handling continues to be handled in same way as before. Additionally process_req() work entry cancels any pending work for a request that gets completed while processing those requests. Originally ib_addr was ST workqueue, but it became MT work queue with patch of [1]. This patch again makes it similar to ST so that neighbour update events handler work item doesn't race with other work items. In one such below trace, (though on 4.5 based kernel) it can be seen that process_req() never executed the callback, which is likely for an event that was schedule by queue_req() when previous callback was getting executed by workqueue. [<ffffffff816b0dde>] schedule+0x3e/0x90 [<ffffffff816b3c45>] schedule_timeout+0x1b5/0x210 [<ffffffff81618c37>] ? ip_route_output_flow+0x27/0x70 [<ffffffffa027f9c9>] ? addr_resolve+0x149/0x1b0 [ib_addr] [<ffffffff816b228f>] wait_for_completion+0x10f/0x170 [<ffffffff810b6140>] ? try_to_wake_up+0x210/0x210 [<ffffffffa027f220>] ? rdma_copy_addr+0xa0/0xa0 [ib_addr] [<ffffffffa0280120>] rdma_addr_find_l2_eth_by_grh+0x1d0/0x278 [ib_addr] [<ffffffff81321297>] ? sub_alloc+0x77/0x1c0 [<ffffffffa02943b7>] ib_init_ah_from_wc+0x3a7/0x5a0 [ib_core] [<ffffffffa0457aba>] cm_req_handler+0xea/0x580 [ib_cm] [<ffffffff81015982>] ? __switch_to+0x212/0x5e0 [<ffffffffa04582fd>] cm_work_handler+0x6d/0x150 [ib_cm] [<ffffffff810a14c1>] process_one_work+0x151/0x4b0 [<ffffffff810a1940>] worker_thread+0x120/0x480 [<ffffffff816b074b>] ? __schedule+0x30b/0x890 [<ffffffff810a1820>] ? process_one_work+0x4b0/0x4b0 [<ffffffff810a1820>] ? process_one_work+0x4b0/0x4b0 [<ffffffff810a6b1e>] kthread+0xce/0xf0 [<ffffffff810a6a50>] ? kthread_freezable_should_stop+0x70/0x70 [<ffffffff816b53a2>] ret_from_fork+0x42/0x70 [<ffffffff810a6a50>] ? kthread_freezable_should_stop+0x70/0x70 INFO: task kworker/u144:1:156520 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kworker/u144:1 D ffff883ffe1d7600 0 156520 2 0x00000080 Workqueue: ib_addr process_req [ib_addr] ffff883f446fbbd8 0000000000000046 ffff881f95280000 ffff881ff24de200 ffff883f66120000 ffff883f446f8008 ffff881f95280000 ffff883f6f9208c4 ffff883f6f9208c8 00000000ffffffff ffff883f446fbbf8 ffffffff816b0dde [1] http://lkml.iu.edu/hypermail/linux/kernel/1608.1/05834.html Signed-off-by: Parav Pandit <parav@mellanox.com> Reviewed-by: Mark Bloch <markb@mellanox.com> Signed-off-by: Leon Romanovsky <leon@kernel.org> Signed-off-by: Doug Ledford <dledford@redhat.com> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.