Documentation: nvme: add an example for nvme fault injection

This adds an example of how to inject errors into admin commands.

Suggested-by: Thomas Tai <thomas.tai@oracle.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Minwoo Im <minwoo.im@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Documentation/fault-injection/nvme-fault-injection.txt

@@ -114,3 +114,59 @@ R13: ffff88011a3c9680 R14: 0000000000000000 R15: 0000000000000000
   cpu_startup_entry+0x6f/0x80
   start_secondary+0x187/0x1e0
   secondary_startup_64+0xa5/0xb0
+
+Example 3: Inject an error into the 10th admin command
+------------------------------------------------------
+
+echo 100 > /sys/kernel/debug/nvme0/fault_inject/probability
+echo 10 > /sys/kernel/debug/nvme0/fault_inject/space
+echo 1 > /sys/kernel/debug/nvme0/fault_inject/times
+nvme reset /dev/nvme0
+
+Expected Result:
+
+After NVMe controller reset, the reinitialization may or may not succeed.
+It depends on which admin command is actually forced to fail.
+
+Message from dmesg:
+
+nvme nvme0: resetting controller
+FAULT_INJECTION: forcing a failure.
+name fault_inject, interval 1, probability 100, space 1, times 1
+CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-rc2+ #2
+Hardware name: MSI MS-7A45/B150M MORTAR ARCTIC (MS-7A45), BIOS 1.50 04/25/2017
+Call Trace:
+ <IRQ>
+ dump_stack+0x63/0x85
+ should_fail+0x14a/0x170
+ nvme_should_fail+0x38/0x80 [nvme_core]
+ nvme_irq+0x129/0x280 [nvme]
+ ? blk_mq_end_request+0xb3/0x120
+ __handle_irq_event_percpu+0x84/0x1a0
+ handle_irq_event_percpu+0x32/0x80
+ handle_irq_event+0x3b/0x60
+ handle_edge_irq+0x7f/0x1a0
+ handle_irq+0x20/0x30
+ do_IRQ+0x4e/0xe0
+ common_interrupt+0xf/0xf
+ </IRQ>
+RIP: 0010:cpuidle_enter_state+0xc5/0x460
+Code: ff e8 8f 5f 86 ff 80 7d c7 00 74 17 9c 58 0f 1f 44 00 00 f6 c4 02 0f 85 69 03 00 00 31 ff e8 62 aa 8c ff fb 66 0f 1f 44 00 00 <45> 85 ed 0f 88 37 03 00 00 4c 8b 45 d0 4c 2b 45 b8 48 ba cf f7 53
+RSP: 0018:ffffffff88c03dd0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffdc
+RAX: ffff9dac25a2ac80 RBX: ffffffff88d53760 RCX: 000000000000001f
+RDX: 0000000000000000 RSI: 000000002d958403 RDI: 0000000000000000
+RBP: ffffffff88c03e18 R08: fffffff75e35ffb7 R09: 00000a49a56c0b48
+R10: ffffffff88c03da0 R11: 0000000000001b0c R12: ffff9dac25a34d00
+R13: 0000000000000006 R14: 0000000000000006 R15: ffffffff88d53760
+ cpuidle_enter+0x2e/0x40
+ call_cpuidle+0x23/0x40
+ do_idle+0x201/0x280
+ cpu_startup_entry+0x1d/0x20
+ rest_init+0xaa/0xb0
+ arch_call_rest_init+0xe/0x1b
+ start_kernel+0x51c/0x53b
+ x86_64_start_reservations+0x24/0x26
+ x86_64_start_kernel+0x74/0x77
+ secondary_startup_64+0xa4/0xb0
+nvme nvme0: Could not set queue count (16385)
+nvme nvme0: IO queues not created