Fix crash in low memory conditions. Usual backtrace looked
like this:
pqisrc_build_sgl() at pqisrc_build_sgl+0x8d/frame 0xfffffe009e8b7a00
pqisrc_build_raid_io() at pqisrc_build_raid_io+0x231/frame 0xfffffe009e8b7a40
pqisrc_build_send_io() at pqisrc_build_send_io+0x375/frame 0xfffffe009e8b7b00
pqi_request_map_helper() at pqi_request_map_helper+0x282/frame 0xfffffe009e8b7ba0
bus_dmamap_load_ccb() at bus_dmamap_load_ccb+0xd7/frame 0xfffffe009e8b7c00
pqi_map_request() at pqi_map_request+0x9b/frame 0xfffffe009e8b7c70
pqisrc_io_start() at pqisrc_io_start+0x55c/frame 0xfffffe009e8b7d50
smartpqi_cam_action() at smartpqi_cam_action+0xb8/frame 0xfffffe009e8b7de0
xpt_run_devq() at xpt_run_devq+0x30a/frame 0xfffffe009e8b7e40
xpt_action_default() at xpt_action_default+0x94b/frame 0xfffffe009e8b7e90
dastart() at dastart+0x33b/frame 0xfffffe009e8b7ee0
xpt_run_allocq() at xpt_run_allocq+0x1a2/frame 0xfffffe009e8b7f30
dastrategy() at dastrategy+0x71/frame 0xfffffe009e8b7f60
g_disk_start() at g_disk_start+0x351/frame 0xfffffe009e8b7fc0
g_io_request() at g_io_request+0x3cf/frame 0xfffffe009e8b8010
g_part_start() at g_part_start+0x120/frame 0xfffffe009e8b8090
g_io_request() at g_io_request+0x3cf/frame 0xfffffe009e8b80e0
zio_vdev_io_start() at zio_vdev_io_start+0x4b2/frame 0xfffffe009e8b8140
zio_execute() at zio_execute+0x17c/frame 0xfffffe009e8b8180
zio_nowait() at zio_nowait+0xc4/frame 0xfffffe009e8b81b0
vdev_queue_io_done() at vdev_queue_io_done+0x138/frame 0xfffffe009e8b81f0
zio_vdev_io_done() at zio_vdev_io_done+0x151/frame 0xfffffe009e8b8220
zio_execute() at zio_execute+0x17c/frame 0xfffffe009e8b8260
taskqueue_run_locked() at taskqueue_run_locked+0x10c/frame 0xfffffe009e8b82c0
taskqueue_thread_loop() at taskqueue_thread_loop+0x88/frame 0xfffffe009e8b82f0
fork_exit() at fork_exit+0x84/frame 0xfffffe009e8b8330
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe009e8b8330
Reviewed by: deepak.ukey_microsemi.com, sbruno
MFC after: 2 weeks
Sponsored by: Klara Inc.
Differential Revision: https://reviews.freebsd.org/D19470