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Subject[PATCH 4/5] bio: fix bio_kmalloc()
Date
Impact: fix bio_kmalloc() and its destruction path

bio_kmalloc() was broken in two ways.

* bvec_alloc_bs() first allocates bvec using kmalloc() and then
ignores it and allocates again like non-kmalloc bvecs.

* bio_kmalloc_destructor() didn't check for and free bio integrity
data.

This patch fixes the above problems. kmalloc patch is separated out
from bio_alloc_bioset() and allocates the requested number of bvecs as
inline bvecs.

* bio_alloc_bioset() no longer takes NULL @bs. None other than
bio_kmalloc() used it and outside users can't know how it was
allocated anyway.

* Define and use BIO_POOL_NONE so that pool index check in
bvec_free_bs() triggers if inline or kmalloc allocated bvec gets
there.

* Relocate destructors on top of each allocation function so that how
they're used is more clear.

Jens Axboe suggested allocating bvecs inline.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <jens.axboe@oracle.com>
---
fs/bio.c | 108 ++++++++++++++++++++++++++-------------------------
include/linux/bio.h | 1 +
2 files changed, 56 insertions(+), 53 deletions(-)
diff --git a/fs/bio.c b/fs/bio.c
index e0c9e54..6c2aef6 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -175,14 +175,6 @@ struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned long *idx,
struct bio_vec *bvl;

/*
- * If 'bs' is given, lookup the pool and do the mempool alloc.
- * If not, this is a bio_kmalloc() allocation and just do a
- * kzalloc() for the exact number of vecs right away.
- */
- if (!bs)
- bvl = kmalloc(nr * sizeof(struct bio_vec), gfp_mask);
-
- /*
* see comment near bvec_array define!
*/
switch (nr) {
@@ -260,21 +252,6 @@ void bio_free(struct bio *bio, struct bio_set *bs)
mempool_free(p, bs->bio_pool);
}

-/*
- * default destructor for a bio allocated with bio_alloc_bioset()
- */
-static void bio_fs_destructor(struct bio *bio)
-{
- bio_free(bio, fs_bio_set);
-}
-
-static void bio_kmalloc_destructor(struct bio *bio)
-{
- if (bio_has_allocated_vec(bio))
- kfree(bio->bi_io_vec);
- kfree(bio);
-}
-
void bio_init(struct bio *bio)
{
memset(bio, 0, sizeof(*bio));
@@ -301,21 +278,15 @@ void bio_init(struct bio *bio)
**/
struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
{
+ unsigned long idx = BIO_POOL_NONE;
struct bio_vec *bvl = NULL;
- struct bio *bio = NULL;
- unsigned long idx = 0;
- void *p = NULL;
-
- if (bs) {
- p = mempool_alloc(bs->bio_pool, gfp_mask);
- if (!p)
- goto err;
- bio = p + bs->front_pad;
- } else {
- bio = kmalloc(sizeof(*bio), gfp_mask);
- if (!bio)
- goto err;
- }
+ struct bio *bio;
+ void *p;
+
+ p = mempool_alloc(bs->bio_pool, gfp_mask);
+ if (unlikely(!p))
+ return NULL;
+ bio = p + bs->front_pad;

bio_init(bio);

@@ -332,22 +303,33 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)

nr_iovecs = bvec_nr_vecs(idx);
}
+out_set:
bio->bi_flags |= idx << BIO_POOL_OFFSET;
bio->bi_max_vecs = nr_iovecs;
-out_set:
bio->bi_io_vec = bvl;
-
return bio;

err_free:
- if (bs)
- mempool_free(p, bs->bio_pool);
- else
- kfree(bio);
-err:
+ mempool_free(p, bs->bio_pool);
return NULL;
}

+static void bio_fs_destructor(struct bio *bio)
+{
+ bio_free(bio, fs_bio_set);
+}
+
+/**
+ * bio_alloc - allocate a new bio, memory pool backed
+ * @gfp_mask: allocation mask to use
+ * @nr_iovecs: number of iovecs
+ *
+ * Allocate a new bio with @nr_iovecs bvecs. If @gfp_mask
+ * contains __GFP_WAIT, the allocation is guaranteed to succeed.
+ *
+ * RETURNS:
+ * Pointer to new bio on success, NULL on failure.
+ */
struct bio *bio_alloc(gfp_t gfp_mask, int nr_iovecs)
{
struct bio *bio = bio_alloc_bioset(gfp_mask, nr_iovecs, fs_bio_set);
@@ -358,19 +340,39 @@ struct bio *bio_alloc(gfp_t gfp_mask, int nr_iovecs)
return bio;
}

-/*
- * Like bio_alloc(), but doesn't use a mempool backing. This means that
- * it CAN fail, but while bio_alloc() can only be used for allocations
- * that have a short (finite) life span, bio_kmalloc() should be used
- * for more permanent bio allocations (like allocating some bio's for
- * initalization or setup purposes).
+static void bio_kmalloc_destructor(struct bio *bio)
+{
+ if (bio_integrity(bio))
+ bio_integrity_free(bio);
+ kfree(bio);
+}
+
+/**
+ * bio_kmalloc - allocate a new bio
+ * @gfp_mask: allocation mask to use
+ * @nr_iovecs: number of iovecs
+ *
+ * Similar to bio_alloc() but uses regular kmalloc for allocation
+ * and can fail unless __GFP_NOFAIL is set in @gfp_mask. This is
+ * useful for more permanant or over-sized bio allocations.
+ *
+ * RETURNS:
+ * Poitner to new bio on success, NULL on failure.
*/
struct bio *bio_kmalloc(gfp_t gfp_mask, int nr_iovecs)
{
- struct bio *bio = bio_alloc_bioset(gfp_mask, nr_iovecs, NULL);
+ struct bio *bio;

- if (bio)
- bio->bi_destructor = bio_kmalloc_destructor;
+ bio = kmalloc(sizeof(struct bio) + nr_iovecs * sizeof(struct bio_vec),
+ gfp_mask);
+ if (unlikely(!bio))
+ return NULL;
+
+ bio_init(bio);
+ bio->bi_flags |= BIO_POOL_NONE << BIO_POOL_OFFSET;
+ bio->bi_max_vecs = nr_iovecs;
+ bio->bi_io_vec = bio->bi_inline_vecs;
+ bio->bi_destructor = bio_kmalloc_destructor;

return bio;
}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index b89cf2d..7b214fd 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -132,6 +132,7 @@ struct bio {
* top 4 bits of bio flags indicate the pool this bio came from
*/
#define BIO_POOL_BITS (4)
+#define BIO_POOL_NONE ((1UL << BIO_POOL_BITS) - 1)
#define BIO_POOL_OFFSET (BITS_PER_LONG - BIO_POOL_BITS)
#define BIO_POOL_MASK (1UL << BIO_POOL_OFFSET)
#define BIO_POOL_IDX(bio) ((bio)->bi_flags >> BIO_POOL_OFFSET)
--
1.6.0.2


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