[PATCH] md/raid5: read batch_head under stripe_lock in make_stripe_request

[Chen Cheng]

From: Chen Cheng <chencheng@xxxxxxxxx>

KCSAN reports race in raid5_make_request() vs. stripe_add_to_batch_list()

write: sh->batch_head = head->batch_head / head
       in stripe_add_to_batch_list() via make_stripe_request()
read:  (!sh->batch_head || sh == sh->batch_head)
       in make_stripe_request()
variable: struct stripe_head::batch_head

sh->batch_head is documented as protected by stripe_lock.

KCSAN report:
  BUG: KCSAN: data-race in raid5_make_request / raid5_make_request

  write to 0xffff8f03062432d8 of 8 bytes by task 210246 on cpu 6:
    raid5_make_request+0x175e/0x2ab0
    md_handle_request+0x2c5/0x700
    md_submit_bio+0x126/0x320
    [.........]
    btrfs_sync_file+0x181/0x970
    vfs_fsync_range+0x71/0x110
    do_fsync+0x46/0xa0
    __x64_sys_fsync+0x20/0x30

  read to 0xffff8f03062432d8 of 8 bytes by task 210251 on cpu 0:
    raid5_make_request+0x7c7/0x2ab0
    md_handle_request+0x2c5/0x700
    md_submit_bio+0x126/0x320
    [.........]
    btrfs_remap_file_range+0x266/0x980
    vfs_clone_file_range+0x16d/0x610
    ioctl_file_clone+0x64/0xd0
    do_vfs_ioctl+0x87f/0xbc0
    __x64_sys_ioctl+0xb8/0x130

  value changed: 0x0000000000000000 -> 0xffff8f0307798728

Signed-off-by: Chen Cheng <chencheng@xxxxxxxxx>
---
 drivers/md/raid5.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5521051a9425..efc63740f867 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6108,14 +6108,16 @@ static enum stripe_result make_stripe_request(struct mddev *mddev,
 		ctx->do_flush = false;
 	}
 
 	set_bit(STRIPE_HANDLE, &sh->state);
 	clear_bit(STRIPE_DELAYED, &sh->state);
+	spin_lock_irq(&sh->stripe_lock);
 	if ((!sh->batch_head || sh == sh->batch_head) &&
 	    (bi->bi_opf & REQ_SYNC) &&
 	    !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
 		atomic_inc(&conf->preread_active_stripes);
+	spin_unlock_irq(&sh->stripe_lock);
 
 	release_stripe_plug(mddev, sh);
 	return STRIPE_SUCCESS;
 
 out_release:
-- 
2.54.0