At 08/22/2016 11:07 PM, Mike Snitzer wrote:
On Mon, Aug 22 2016 at 4:05am -0400,
Lukas Herbolt <lherbolt@xxxxxxxxxx> wrote:
Hello,
There is patch from Mike. It's part of current pull request to 4.8-rc1
For more details check:
- https://www.redhat.com/archives/dm-devel/2016-July/msg00561.html
- https://www.redhat.com/archives/dm-devel/2016-August/msg00109.html
Lukas
On Mon, Aug 22, 2016 at 9:31 AM, Qu Wenruo <quwenruo@xxxxxxxxxxxxxx> wrote:
Hi, Mike and btrfs and dm guys
When doing regression test on v4.8-rc1, we found that fstests/btrfs/056
always fails. With the following dmesg:
---
Buffer I/O error on dev dm-0, logical block 1310704, async page read
Buffer I/O error on dev dm-0, logical block 16, async page read
Buffer I/O error on dev dm-0, logical block 16, async page read
---
And bisect leads to the following commits:
---
commit 99f3c90d0d85708e7401a81ce3314e50bf7f2819
Author: Mike Snitzer <snitzer@xxxxxxxxxx>
Date: Fri Jul 29 13:19:55 2016 -0400
dm flakey: error READ bios during the down_interval
---
While according to the document of dm-flakey, it says that when using
drop_writes feature, read bios are not affected:
---
drop_writes:
All write I/O is silently ignored.
Read I/O is handled correctly.
I went back to the dm-flakey.c code at the time that the 'drop_writes'
feature was added via commit b26f5e3d. It does confirm your
understanding of how reads should be handled if drop_writes is enabled.
Not sure why I thought differently. Please try the following patch.
In fact, I quite understand the idea to corrupt READ bio, if drop_writes
and corrupt_bio_byte is given at the same time.
diff --git a/drivers/md/dm-flakey.c b/drivers/md/dm-flakey.c
index 97e446d..6a2e8dd 100644
--- a/drivers/md/dm-flakey.c
+++ b/drivers/md/dm-flakey.c
@@ -289,15 +289,13 @@ static int flakey_map(struct dm_target *ti, struct bio *bio)
pb->bio_submitted = true;
/*
- * Map reads as normal only if corrupt_bio_byte set.
+ * Error reads if neither corrupt_bio_byte or drop_writes are set.
+ * Otherwise, flakey_end_io() will decide if the reads should be modified.
*/
if (bio_data_dir(bio) == READ) {
- /* If flags were specified, only corrupt those that match. */
- if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == READ) &&
- all_corrupt_bio_flags_match(bio, fc))
- goto map_bio;
- else
+ if (!fc->corrupt_bio_byte && !test_bit(DROP_WRITES, &fc->flags))
return -EIO;
+ goto map_bio;
}
/*
@@ -334,14 +332,21 @@ static int flakey_end_io(struct dm_target *ti, struct bio *bio, int error)
struct flakey_c *fc = ti->private;
struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
- /*
- * Corrupt successful READs while in down state.
- */
if (!error && pb->bio_submitted && (bio_data_dir(bio) == READ)) {
- if (fc->corrupt_bio_byte)
+ if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == READ) &&
+ all_corrupt_bio_flags_match(bio, fc)) {
+ /*
+ * Corrupt successful matching READs while in down state.
+ */
corrupt_bio_data(bio, fc);
- else
+
+ } else if (!test_bit(DROP_WRITES, &fc->flags)) {
+ /*
+ * Error read during the down_interval if drop_writes
+ * wasn't configured.
+ */
return -EIO;
+ }
}
return error;
It looks good to me, as it can also handle corrupt_bio_byte and drop_writes.
Tested-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Thanks,
Qu
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