When md raid device (e.g. raid456) is used as backing device, read-ahead requests on a degrading and recovering md raid device might be failured immediately by md raid code, but indeed this md raid array can still be read or write for normal I/O requests. Therefore such failed read-ahead request are not real hardware failure. Further more, after degrading and recovering accomplished, read-ahead requests will be handled by md raid array again.

For such condition, I/O failures of read-ahead requests don't indicate real health status (because normal I/O still be served), they should not be counted into I/O error counter dc->io_errors.

Since there is no simple way to detect whether the backing divice is a md raid device, this patch simply ignores I/O failures for read-ahead bios on backing device, to avoid bogus backing device failure on a degrading md raid array.

Suggested-and-tested-by: Thorsten Knabe linux@thorsten-knabe.de Signed-off-by: Coly Li colyli@suse.de Cc: stable@vger.kernel.org --- drivers/md/bcache/io.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c index c25097968319..4d93f07f63e5 100644 --- a/drivers/md/bcache/io.c +++ b/drivers/md/bcache/io.c @@ -58,6 +58,18 @@ void bch_count_backing_io_errors(struct cached_dev *dc, struct bio *bio)

WARN_ONCE(!dc, "NULL pointer of struct cached_dev");

+ /* + * Read-ahead requests on a degrading and recovering md raid + * (e.g. raid6) device might be failured immediately by md + * raid code, which is not a real hardware media failure. So + * we shouldn't count failed REQ_RAHEAD bio to dc->io_errors. + */ + if (bio->bi_opf & REQ_RAHEAD) { + pr_warn_ratelimited("%s: Read-ahead I/O failed on backing device, ignore", + dc->backing_dev_name); + return; + } + errors = atomic_add_return(1, &dc->io_errors); if (errors < dc->error_limit) pr_err("%s: IO error on backing device, unrecoverable",