[PATCH RFC v3 1/1] mtd_blkdevs: avoid soft lockups with some mtd/spi devices

[Miquel Raynal]

On Wed, 2022-01-26 at 10:11:20 UTC, David Decotigny wrote:
> From: David Decotigny <ddecotig at google.com>
> 
> With some spi devices, the heavy cpu usage due to polling the spi
> registers may lead to netdev timeouts, RCU complaints, etc. This can
> be acute in the absence of CONFIG_PREEMPT. This patch allows to give
> enough breathing room to avoid those incorrectly detected netdev
> timeouts for example.
> 
> Example splat on 5.10.92:
> [  828.399306] rcu: INFO: rcu_sched self-detected stall on CPU
> ...
> [  828.419245] Task dump for CPU 1:
> [  828.422465] task:kworker/1:1H    state:R  running task on cpu   1   stack:    0 pid:   76 ppid:     2 flags:0x0000002a
> [  828.433132] Workqueue: kblockd blk_mq_run_work_fn
> [  828.437820] Call trace:
> ...
> [  828.512267]  spi_mem_exec_op+0x4d0/0xde0
> [  828.516184]  spi_mem_dirmap_read+0x180/0x39c
> [  828.520443]  spi_nor_read_data+0x428/0x7e8
> [  828.524523]  spi_nor_read+0x154/0x214
> [  828.528172]  mtd_read_oob+0x440/0x714
> [  828.531815]  mtd_read+0xac/0x120
> [  828.535030]  mtdblock_readsect+0x178/0x230
> [  828.539102]  mtd_blktrans_work+0x9fc/0xf28
> [  828.543177]  mtd_queue_rq+0x1ac/0x2e4
> [  828.546827]  blk_mq_dispatch_rq_list+0x2cc/0xa44
> [  828.551419]  blk_mq_do_dispatch_sched+0xb0/0x7cc
> [  828.556010]  __blk_mq_sched_dispatch_requests+0x350/0x494
> [  828.561372]  blk_mq_sched_dispatch_requests+0xac/0xe4
> [  828.566387]  __blk_mq_run_hw_queue+0x130/0x254
> [  828.570806]  blk_mq_run_work_fn+0x50/0x60
> [  828.574814]  process_one_work+0x578/0xf1c
> [  828.578814]  worker_thread+0x5dc/0xea0
> [  828.582547]  kthread+0x270/0x2d4
> [  828.585765]  ret_from_fork+0x10/0x30
> 
> 
> Signed-off-by: David Decotigny <ddecotig at google.com>
> Reviewed-by: Richard Weinberger <richard at nod.at>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel