On 2021-05-24 19:41, Paolo Valente wrote:
Il giorno 24 mag 2021, alle ore 19:13, Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx> ha scritto:
On 2021-05-24 18:57, Paolo Valente wrote:
Il giorno 20 mag 2021, alle ore 09:15, Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx> ha scritto:
On 2021-05-18 12:43, Luca Mariotti wrote:
When attempting to schedule a merge of a given bfq_queue with the currently
in-service bfq_queue or with a cooperating bfq_queue among the scheduled
bfq_queues, delayed stable merge is checked for rotational or non-queueing
devs. For this stable merge to be performed, some conditions must be met.
If the current bfq_queue underwent some split from some merged bfq_queue,
one of these conditions is that two hundred milliseconds must elapse from
split, otherwise this condition is always met.
Unfortunately, by mistake, time_is_after_jiffies() was written instead of
time_is_before_jiffies() for this check, verifying that less than two
hundred milliseconds have elapsed instead of verifying that at least two
hundred milliseconds have elapsed.
Fix this issue by replacing time_is_after_jiffies() with
time_is_before_jiffies().
Signed-off-by: Luca Mariotti <mariottiluca1@xxxxxxxxxx>
Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
Signed-off-by: Pietro Pedroni <pedroni.pietro.96@xxxxxxxxx>
---
block/bfq-iosched.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index acd1f881273e..2adb1e69c9d2 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2697,7 +2697,7 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
if (unlikely(!bfqd->nonrot_with_queueing)) {
if (bic->stable_merge_bfqq &&
!bfq_bfqq_just_created(bfqq) &&
- time_is_after_jiffies(bfqq->split_time +
+ time_is_before_jiffies(bfqq->split_time +
msecs_to_jiffies(200))) {
struct bfq_queue *stable_merge_bfqq =
bic->stable_merge_bfqq;
Not sure why but with this patch I quickly got a division-by-zero in BFQ and
complete system halt. Unfortunately I couldn't capture the exact stack trace,
but it read something like bfq_calc_weight() or something ike that.
I looked through the code and found bfq_delta(), so maybe weight got
reduced to 0?
Hi Holger,
is this (easily) reproducible for you? If so, I'd like to propose you
a candidate fix.
Yes, it's easily reproducible (should be reproducible on 5.13-rc as well).
Simple read/write I/O on a cold FS (rotational disk obviously) will crash
pretty much immediately; without it everything works fine, likely because the
bug (in the recent queue merging patches?) is never triggered due to the
accidentally-wrong time calculation.
Exactly!
Unfortunately, no crash happens on my systems. Or, actually, crashes
stopped after the attached fix.
Will gladly test your patch! :)
Here it is!
I'll make a proper commit after your early tests.
Crossing my fingers,
Paolo
That did it - it now survived a bunch of heavy read/write/mixed I/O that
would previously crash right away. Maybe it's because btrfs uses several
workers and so different IOs got mixed together? Anyway:
Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues")
Tested-by: Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx>
Thanks!
Holger
