[PATCH 1/7] cxlflash: Yield to active send threads

[Matthew R. Ochs]

On Fri, May 11, 2018 at 02:04:46PM -0500, Uma Krishnan wrote:
> The following Oops may be encountered if the device is reset, i.e. EEH
> recovery, while there is heavy I/O traffic:
> 
> 59:mon> t
> [c000200db64bb680] c008000009264c40 cxlflash_queuecommand+0x3b8/0x500
> 					[cxlflash]
> [c000200db64bb770] c00000000090d3b0 scsi_dispatch_cmd+0x130/0x2f0
> [c000200db64bb7f0] c00000000090fdd8 scsi_request_fn+0x3c8/0x8d0
> [c000200db64bb900] c00000000067f528 __blk_run_queue+0x68/0xb0
> [c000200db64bb930] c00000000067ab80 __elv_add_request+0x140/0x3c0
> [c000200db64bb9b0] c00000000068daac blk_execute_rq_nowait+0xec/0x1a0
> [c000200db64bba00] c00000000068dbb0 blk_execute_rq+0x50/0xe0
> [c000200db64bba50] c0000000006b2040 sg_io+0x1f0/0x520
> [c000200db64bbaf0] c0000000006b2e94 scsi_cmd_ioctl+0x534/0x610
> [c000200db64bbc20] c000000000926208 sd_ioctl+0x118/0x280
> [c000200db64bbcc0] c00000000069f7ac blkdev_ioctl+0x7fc/0xe30
> [c000200db64bbd20] c000000000439204 block_ioctl+0x84/0xa0
> [c000200db64bbd40] c0000000003f8514 do_vfs_ioctl+0xd4/0xa00
> [c000200db64bbde0] c0000000003f8f04 SyS_ioctl+0xc4/0x130
> [c000200db64bbe30] c00000000000b184 system_call+0x58/0x6c
> 
> When there is no room to send the I/O request, the cached room is refreshed
> by reading the memory mapped command room value from the AFU. The AFU
> register mapping is refreshed during a reset, creating a race condition
> that can lead to the Oops above.
> 
> During a device reset, the AFU should not be unmapped until all the active
> send threads quiesce. An atomic counter, cmds_active, is currently used to
> track internal AFU commands and quiesce during reset. This same counter can
> also be used for the active send threads.
> 
> Signed-off-by: Uma Krishnan <ukrishn at linux.vnet.ibm.com>

Acked-by: Matthew R. Ochs <mrochs at linux.vnet.ibm.com>