Re: [PATCH] md/raid1,raid10: don't pass down the REQ_RAHEAD flag

[Yu Kuai]

Hi,

在 2025/05/19 19:19, Yu Kuai 写道:
The commit e879a0d9cb08 ("md/raid1,raid10: don't ignore IO flags") breaks
the lvm2 test shell/lvcreate-large-raid.sh. The commit changes raid1 and
raid10 to pass down all the flags from the incoming bio. The problem is
when we pass down the REQ_RAHEAD flag - bios with this flag may fail
anytime and md-raid is not prepared to handle this failure.

Can dm-raid handle this falg? At least from md-raid array, for read
ahead IO, it doesn't make sense to kill that flag.

If we want to fall back to old behavior, can we kill that flag from
dm-raid?

Please ignore the last reply, I misunderstand your commit message, I
thought you said dm-raid, actually you said mdraid, and it's correct,
if read_bio faild raid1/10 will set badblocks which is not expected.

Then for reada head IO, I still think don't kill REQ_RAHEAD for
underlying disks is better, what do you think about skip handling IO
error for ead ahead IO?

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 657d481525be..b8b4fead31f3 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -380,7 +380,10 @@ static void raid1_end_read_request(struct bio *bio)
                /* This was a fail-fast read so we definitely
                 * want to retry */
                ;
-       else {
+       else if (bio->bi_opf & REQ_RAHEAD) {
+               /* don't handle readahead error, which can fail at 
anytime. */
+               uptodate = 1;
+       } else {
                /* If all other devices have failed, we want to return
                 * the error upwards rather than fail the last device.
                 * Here we redefine "uptodate" to mean "Don't want to 
retry"
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index dce06bf65016..4d51aaf3b39b 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -399,6 +399,9 @@ static void raid10_end_read_request(struct bio *bio)
                 * wait for the 'master' bio.
                 */
                set_bit(R10BIO_Uptodate, &r10_bio->state);
+       } else if (bio->bi_opf & REQ_RAHEAD) {
+               /* don't handle readahead error, which can fail at 
anytime. */
+               uptodate = 1;
        } else {
                /* If all other devices that store this block have
                 * failed, we want to return the error upwards rather

Thanks,
Kuai