Messages in this thread Patch in this message | | | Date | Tue, 3 May 2011 14:05:26 -0400 | From | Christoph Hellwig <> | Subject | Re: merging discard request in the block layer |
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I finally maged to debug this a bit further and can have found a cure for the null pointer derefences I got on recent kernels.
The problem is that bio_has_data thinks discard requests have a payload and thus tries to poke into it's pages when trying to merge requests. Taking the REQ_DISCARD check in to bio_has_data fixes that. I've also tried to special case discard requests in bio_cur_bytes, but that doesn't fix the botched requests messages yet. I suspect the merging code might need some additions to update the bio_size for discard requests that it currently skips.
Index: xfs/block/blk-core.c =================================================================== --- xfs.orig/block/blk-core.c 2011-05-03 19:45:51.980219652 +0200 +++ xfs/block/blk-core.c 2011-05-03 19:47:51.756237436 +0200 @@ -1645,7 +1645,7 @@ void submit_bio(int rw, struct bio *bio) * If it's a regular read/write or a barrier with data attached, * go through the normal accounting stuff before submission. */ - if (bio_has_data(bio) && !(rw & REQ_DISCARD)) { + if (bio_has_data(bio)) { if (rw & WRITE) { count_vm_events(PGPGOUT, count); } else { Index: xfs/include/linux/bio.h =================================================================== --- xfs.orig/include/linux/bio.h 2011-05-03 19:43:28.537663414 +0200 +++ xfs/include/linux/bio.h 2011-05-03 19:48:18.632758500 +0200 @@ -69,7 +69,7 @@ static inline unsigned int bio_cur_bytes(struct bio *bio) { - if (bio->bi_vcnt) + if (bio->bi_vcnt && !(bio->bi_rw & REQ_DISCARD)) return bio_iovec(bio)->bv_len; else /* dataless requests such as discard */ return bio->bi_size; @@ -368,7 +368,7 @@ static inline char *__bio_kmap_irq(struc */ static inline int bio_has_data(struct bio *bio) { - return bio && bio->bi_io_vec != NULL; + return bio && bio->bi_io_vec != NULL && !(bio->bi_rw & REQ_DISCARD); } /*
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