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dm: safely allocate multiple bioset bios

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DM targets can request multiple bios be sent to them by DM core (see:
num_{flush,discard,write_same,write_zeroes}_bios).  But until now these
bios were allocated in an unsafe manner than could potentially exhaust
the DM device's bioset -- in the face of multiple threads each trying to
do multiple allocations from the same DM device's bioset.

Fix __send_duplicate_bios() by using the new alloc_multiple_bios().  The
allocation strategy used by alloc_multiple_bios() models that used by
dm-crypt.c:crypt_alloc_buffer().

Neil Brown initially proposed this fix but the implementation has been
revised enough that it inappropriate to attribute the entirety of it to
him.

Suggested-by: NeilBrown <neilb@suse.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer 2017-11-22 14:56:12 -05:00
parent f31c21e436
commit 318716ddea
1 changed files with 58 additions and 13 deletions
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71
drivers/md/dm.c
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@ -1264,16 +1264,17 @@ static int clone_bio(struct dm_target_io *tio, struct bio *bio,
return 0;
}
static struct dm_target_io *alloc_tio(struct clone_info *ci,
struct dm_target *ti,
unsigned target_bio_nr)
static struct dm_target_io *alloc_tio(struct clone_info *ci, struct dm_target *ti,
unsigned target_bio_nr, gfp_t gfp_mask)
{
struct dm_target_io *tio;
struct bio *clone;
clone = bio_alloc_bioset(GFP_NOIO, 0, ci->md->bs);
tio = container_of(clone, struct dm_target_io, clone);
clone = bio_alloc_bioset(gfp_mask, 0, ci->md->bs);
if (!clone)
return NULL;
tio = container_of(clone, struct dm_target_io, clone);
tio->io = ci->io;
tio->ti = ti;
tio->target_bio_nr = target_bio_nr;
@ -1281,11 +1282,49 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci,
return tio;
}
static void __clone_and_map_simple_bio(struct clone_info *ci,
struct dm_target *ti,
unsigned target_bio_nr, unsigned *len)
static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,
struct dm_target *ti, unsigned num_bios)
{
struct dm_target_io *tio;
int try;
if (!num_bios)
return;
if (num_bios == 1) {
tio = alloc_tio(ci, ti, 0, GFP_NOIO);
bio_list_add(blist, &tio->clone);
return;
}
for (try = 0; try < 2; try++) {
int bio_nr;
struct bio *bio;
if (try)
mutex_lock(&ci->md->table_devices_lock);
for (bio_nr = 0; bio_nr < num_bios; bio_nr++) {
tio = alloc_tio(ci, ti, bio_nr, try ? GFP_NOIO : GFP_NOWAIT);
if (!tio)
break;
bio_list_add(blist, &tio->clone);
}
if (try)
mutex_unlock(&ci->md->table_devices_lock);
if (bio_nr == num_bios)
return;
while ((bio = bio_list_pop(blist))) {
tio = container_of(bio, struct dm_target_io, clone);
free_tio(tio);
}
}
}
static void __clone_and_map_simple_bio(struct clone_info *ci,
struct dm_target_io *tio, unsigned *len)
{
struct dm_target_io *tio = alloc_tio(ci, ti, target_bio_nr);
struct bio *clone = &tio->clone;
tio->len_ptr = len;
@ -1300,10 +1339,16 @@ static void __clone_and_map_simple_bio(struct clone_info *ci,
static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
unsigned num_bios, unsigned *len)
{
unsigned target_bio_nr;
struct bio_list blist = BIO_EMPTY_LIST;
struct bio *bio;
struct dm_target_io *tio;
for (target_bio_nr = 0; target_bio_nr < num_bios; target_bio_nr++)
__clone_and_map_simple_bio(ci, ti, target_bio_nr, len);
alloc_multiple_bios(&blist, ci, ti, num_bios);
while ((bio = bio_list_pop(&blist))) {
tio = container_of(bio, struct dm_target_io, clone);
__clone_and_map_simple_bio(ci, tio, len);
}
}
static int __send_empty_flush(struct clone_info *ci)
@ -1325,7 +1370,7 @@ static int __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,
struct dm_target_io *tio;
int r;
tio = alloc_tio(ci, ti, 0);
tio = alloc_tio(ci, ti, 0, GFP_NOIO);
tio->len_ptr = len;
r = clone_bio(tio, bio, sector, *len);
if (r < 0) {