@@ -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",
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(+)