btrfs: scrub: update last_physical after scrubbing one stripe

Currently sctx->stat.last_physical only got updated in the following
cases:

- When the last stripe of a non-RAID56 chunk is scrubbed
  This implies a pitfall, if the last stripe is at the chunk boundary,
  and we finished the scrub of the whole chunk, we won't update
  last_physical at all until the next chunk.

- When a P/Q stripe of a RAID56 chunk is scrubbed

This leads the following two problems:

- sctx->stat.last_physical is not updated for a almost full chunk
  This is especially bad, affecting scrub resume, as the resume would
  start from last_physical, causing unnecessary re-scrub.

- "btrfs scrub status" will not report any progress for a long time

Fix the problem by properly updating @last_physical after each stripe is
scrubbed.

And since we're here, for the sake of consistency, use spin lock to
protect the update of @last_physical, just like all the remaining
call sites touching sctx->stat.
Reported-by: Michel Palleau <michel.palleau@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAMFk-+igFTv2E8svg=cQ6o3e6CrR5QwgQ3Ok9EyRaEvvthpqCQ@mail.gmail.com/Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/scrub.c

@@ -1875,6 +1875,9 @@ static int flush_scrub_stripes(struct scrub_ctx *sctx)
 		stripe = &sctx->stripes[i];
 
 		wait_scrub_stripe_io(stripe);
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.last_physical = stripe->physical + stripe_length(stripe);
+		spin_unlock(&sctx->stat_lock);
 		scrub_reset_stripe(stripe);
 	}
 out:
@@ -2143,7 +2146,9 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
 					 cur_physical, &found_logical);
 		if (ret > 0) {
 			/* No more extent, just update the accounting */
+			spin_lock(&sctx->stat_lock);
 			sctx->stat.last_physical = physical + logical_length;
+			spin_unlock(&sctx->stat_lock);
 			ret = 0;
 			break;
 		}
@@ -2340,6 +2345,10 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
 			stripe_logical += chunk_logical;
 			ret = scrub_raid56_parity_stripe(sctx, scrub_dev, bg,
 							 map, stripe_logical);
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.last_physical = min(physical + BTRFS_STRIPE_LEN,
+						       physical_end);
+			spin_unlock(&sctx->stat_lock);
 			if (ret)
 				goto out;
 			goto next;