On Tuesday June 24, mpatocka@xxxxxxxxxx wrote:Hi
bio_endio calls bi_end_io callback. In case of stacked devices (raid, dm),
bio_end_io may call bio_endio again, up to an unspecified length.
The crash because of stack overflow was really observed on sparc64. And
this recursion was one of the contributing factors (using 9 stack frames
--- that is 1728 bytes).
This patch removes the recursion.
This is very cool, thanks! A close mirror of the recursion
avoidance in generic_make_request.
You use a per-cpu queue were generic_make_request uses a per-task
queue. This is fitting as bi_end_io doesn't have a process context,
but is supposed to be fast and able to run with interrupts disabled,
so tying to a cpu is no problem.
--+
+ bio_queue = NULL;
+queue_empty_next_bio:
+ *bio_end_queue_ptr = &bio_queue;
+next_bio:
+
if (error)
clear_bit(BIO_UPTODATE, &bio->bi_flags);
else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
@@ -1175,6 +1196,17 @@
if (bio->bi_end_io)
bio->bi_end_io(bio, error);
+
+ if (bio_queue) {
+ bio = bio_queue;
+ bio_queue = bio->bi_next;
+ if (!bio_queue) goto queue_empty_next_bio;
+ goto next_bio;
checkpatch.pl doesn't like that:
ERROR: trailing statements should be on next line
and I don't either. I would not bother with the mini-optimisation at
all.
Discard the queue_empty_next_bio label and replace the "if () goto"
with
if (!bio_queue)
*bio_end_queue_ptr = &bio_queue;
and leave gcc to optimise the assignment if it wants to.
Reviewed-by: NeilBrown <neilb@xxxxxxx>
Thanks,
NeilBrown