[PATCH] block: Fix cloning of requests with a special payload

[Bart Van Assche <bart.vanassche@xxxxxxx>]

This patch avoids that removing a path controlled by the dm-mpath driver
while mkfs is running triggers the following kernel bug:

    kernel BUG at block/blk-core.c:3347!
    invalid opcode: 0000 [#1] PREEMPT SMP KASAN
    CPU: 20 PID: 24369 Comm: mkfs.ext4 Not tainted 4.18.0-rc1-dbg+ #2
    RIP: 0010:blk_end_request_all+0x68/0x70
    Call Trace:
     <IRQ>
     dm_softirq_done+0x326/0x3d0 [dm_mod]
     blk_done_softirq+0x19b/0x1e0
     __do_softirq+0x128/0x60d
     irq_exit+0x100/0x110
     smp_call_function_single_interrupt+0x90/0x330
     call_function_single_interrupt+0xf/0x20
     </IRQ>

Fixes: f9d03f96b988 ("block: improve handling of the magic discard payload")
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 block/blk-core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 118dd17eb71f..f1e07ed1513c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3529,6 +3529,10 @@ static void __blk_rq_prep_clone(struct request *dst, struct request *src)
 	dst->cpu = src->cpu;
 	dst->__sector = blk_rq_pos(src);
 	dst->__data_len = blk_rq_bytes(src);
+	if (src->rq_flags & RQF_SPECIAL_PAYLOAD) {
+		dst->rq_flags |= RQF_SPECIAL_PAYLOAD;
+		dst->special_vec = src->special_vec;
+	}
 	dst->nr_phys_segments = src->nr_phys_segments;
 	dst->ioprio = src->ioprio;
 	dst->extra_len = src->extra_len;
-- 
2.17.1