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-rw-r--r--block/ll_rw_blk.c53
-rw-r--r--include/linux/sched.h4
2 files changed, 56 insertions, 1 deletions
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 17e18897342..74a567afb83 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -3116,7 +3116,7 @@ static inline int should_fail_request(struct bio *bio)
* bi_sector for remaps as it sees fit. So the values of these fields
* should NOT be depended on after the call to generic_make_request.
*/
-void generic_make_request(struct bio *bio)
+static inline void __generic_make_request(struct bio *bio)
{
request_queue_t *q;
sector_t maxsector;
@@ -3215,6 +3215,57 @@ end_io:
} while (ret);
}
+/*
+ * We only want one ->make_request_fn to be active at a time,
+ * else stack usage with stacked devices could be a problem.
+ * So use current->bio_{list,tail} to keep a list of requests
+ * submited by a make_request_fn function.
+ * current->bio_tail is also used as a flag to say if
+ * generic_make_request is currently active in this task or not.
+ * If it is NULL, then no make_request is active. If it is non-NULL,
+ * then a make_request is active, and new requests should be added
+ * at the tail
+ */
+void generic_make_request(struct bio *bio)
+{
+ if (current->bio_tail) {
+ /* make_request is active */
+ *(current->bio_tail) = bio;
+ bio->bi_next = NULL;
+ current->bio_tail = &bio->bi_next;
+ return;
+ }
+ /* following loop may be a bit non-obvious, and so deserves some
+ * explanation.
+ * Before entering the loop, bio->bi_next is NULL (as all callers
+ * ensure that) so we have a list with a single bio.
+ * We pretend that we have just taken it off a longer list, so
+ * we assign bio_list to the next (which is NULL) and bio_tail
+ * to &bio_list, thus initialising the bio_list of new bios to be
+ * added. __generic_make_request may indeed add some more bios
+ * through a recursive call to generic_make_request. If it
+ * did, we find a non-NULL value in bio_list and re-enter the loop
+ * from the top. In this case we really did just take the bio
+ * of the top of the list (no pretending) and so fixup bio_list and
+ * bio_tail or bi_next, and call into __generic_make_request again.
+ *
+ * The loop was structured like this to make only one call to
+ * __generic_make_request (which is important as it is large and
+ * inlined) and to keep the structure simple.
+ */
+ BUG_ON(bio->bi_next);
+ do {
+ current->bio_list = bio->bi_next;
+ if (bio->bi_next == NULL)
+ current->bio_tail = &current->bio_list;
+ else
+ bio->bi_next = NULL;
+ __generic_make_request(bio);
+ bio = current->bio_list;
+ } while (bio);
+ current->bio_tail = NULL; /* deactivate */
+}
+
EXPORT_SYMBOL(generic_make_request);
/**
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17b72d88c4c..e38c436ee12 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -88,6 +88,7 @@ struct sched_param {
struct exec_domain;
struct futex_pi_state;
+struct bio;
/*
* List of flags we want to share for kernel threads,
@@ -1014,6 +1015,9 @@ struct task_struct {
/* journalling filesystem info */
void *journal_info;
+/* stacked block device info */
+ struct bio *bio_list, **bio_tail;
+
/* VM state */
struct reclaim_state *reclaim_state;