PATCH odd code in bio_add_page

PATCH odd code in bio_add_page

[Neil Brown]

I was just taking a closer look at bio_add_page and there is some code
that doesn't mage sense.  The following patch explains the problem and
suggests a possible fix.

NeilBrown


==================================================
Fix strange code in bio_add_page

With the current code in bio_add_page, if fail_segments is ever set,
it stays set, so bio_add_page will eventually fail having recounted
the segmentation once.

I don't think this is intended.  This patch changes the code to allow
success if the recounting the segments helps.


 ----------- Diffstat output ------------
 ./fs/bio.c |   11 ++++-------
 1 files changed, 4 insertions(+), 7 deletions(-)

diff ./fs/bio.c~current~ ./fs/bio.c
--- ./fs/bio.c~current~	2003-08-26 12:38:15.000000000 +1000
+++ ./fs/bio.c	2003-08-26 12:41:45.000000000 +1000
@@ -296,7 +296,7 @@ int bio_add_page(struct bio *bio, struct
 		 unsigned int offset)
 {
 	request_queue_t *q = bdev_get_queue(bio->bi_bdev);
-	int fail_segments = 0, retried_segments = 0;
+	int retried_segments = 0;
 	struct bio_vec *bvec;
 
 	/*
@@ -315,18 +315,15 @@ int bio_add_page(struct bio *bio, struct
 	 * we might lose a segment or two here, but rather that than
 	 * make this too complex.
 	 */
-retry_segments:
-	if (bio_phys_segments(q, bio) >= q->max_phys_segments
-	    || bio_hw_segments(q, bio) >= q->max_hw_segments)
-		fail_segments = 1;
 
-	if (fail_segments) {
+	while (bio_phys_segments(q, bio) >= q->max_phys_segments
+	    || bio_hw_segments(q, bio) >= q->max_hw_segments) {
+
 		if (retried_segments)
 			return 0;
 
 		bio->bi_flags &= ~(1 << BIO_SEG_VALID);
 		retried_segments = 1;
-		goto retry_segments;
 	}
 
 	/*

Re: PATCH odd code in bio_add_page

[Jens Axboe]

On Tue, Aug 26 2003, Neil Brown wrote:
> 
> I was just taking a closer look at bio_add_page and there is some code
> that doesn't mage sense.  The following patch explains the problem and
> suggests a possible fix.
> 
> NeilBrown
> 
> 
> ==================================================
> Fix strange code in bio_add_page
> 
> With the current code in bio_add_page, if fail_segments is ever set,
> it stays set, so bio_add_page will eventually fail having recounted
> the segmentation once.
> 
> I don't think this is intended.  This patch changes the code to allow
> success if the recounting the segments helps.

Good catch Neil, I agree with the fix.

-- 
Jens Axboe