[Drbd-dev] Re: [Ocfs2-devel] Fixing cluster/heartbeat.c's use of
bio_add_page()
Philipp Reisner
philipp.reisner at linbit.com
Thu Jan 11 10:58:10 CET 2007
[...]
>
> You changed o2hb_bio_wait_init() to initialize wc_num_reqs to zero, and
> instead you increment the value before each submit_bio(). This makes sense
> because we now don't know how many requests will ultimately be submitted.
>
> However, A race now exists here between the piecemeal increment of
> wc_num_reqs and the completion code in o2hb_bio_wait_dec():
>
> if (atomic_dec_and_test(&wc->wc_num_reqs)) {
> BUG_ON(num > 0);
> complete(&wc->wc_io_complete);
> }
>
> So, if enough bios complete before you're done submitting all your read
> requests, you could trigger the completion, wc_io_complete early.
>
> This would certainly be hard to hit, but that's never stopped a race from
> occuring before :)
>
Right, here is a new version of the patch. Now wc_num_reqs gets initialized
to one, and the final decrement happens in o2hb_wait_on_io()
My try of a 'The perfect patch':
Moved the bio_put() call into the bio's bi_end_io() function. This makes the
whole idea of trying to predict the behaviour of bio_add_page() unnecessary.
Removed compute_max_sectors() and o2hb_compute_request_limits().
Signed-off-by: Philipp Reisner <philipp.reisner at linbit.com>
--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c
@@ -184,10 +184,9 @@ static void o2hb_disarm_write_timeout(st
flush_scheduled_work();
}
-static inline void o2hb_bio_wait_init(struct o2hb_bio_wait_ctxt *wc,
- unsigned int num_ios)
+static inline void o2hb_bio_wait_init(struct o2hb_bio_wait_ctxt *wc)
{
- atomic_set(&wc->wc_num_reqs, num_ios);
+ atomic_set(&wc->wc_num_reqs, 1);
init_completion(&wc->wc_io_complete);
wc->wc_error = 0;
}
@@ -212,6 +211,7 @@ static void o2hb_wait_on_io(struct o2hb_
struct address_space *mapping = reg->hr_bdev->bd_inode->i_mapping;
blk_run_address_space(mapping);
+ o2hb_bio_wait_dec(wc, 1);
wait_for_completion(&wc->wc_io_complete);
}
@@ -231,6 +231,7 @@ static int o2hb_bio_end_io(struct bio *b
return 1;
o2hb_bio_wait_dec(wc, 1);
+ bio_put(bio);
return 0;
}
@@ -238,23 +239,22 @@ static int o2hb_bio_end_io(struct bio *b
* start_slot. */
static struct bio *o2hb_setup_one_bio(struct o2hb_region *reg,
struct o2hb_bio_wait_ctxt *wc,
- unsigned int start_slot,
- unsigned int num_slots)
+ unsigned int *current_slot,
+ unsigned int max_slots)
{
- int i, nr_vecs, len, first_page, last_page;
+ int len, current_page;
unsigned int vec_len, vec_start;
unsigned int bits = reg->hr_block_bits;
unsigned int spp = reg->hr_slots_per_page;
+ unsigned int cs = *current_slot;
struct bio *bio;
struct page *page;
- nr_vecs = (num_slots + spp - 1) / spp;
-
/* Testing has shown this allocation to take long enough under
* GFP_KERNEL that the local node can get fenced. It would be
* nicest if we could pre-allocate these bios and avoid this
* all together. */
- bio = bio_alloc(GFP_ATOMIC, nr_vecs);
+ bio = bio_alloc(GFP_ATOMIC, 16);
if (!bio) {
mlog(ML_ERROR, "Could not alloc slots BIO!\n");
bio = ERR_PTR(-ENOMEM);
@@ -262,137 +262,53 @@ static struct bio *o2hb_setup_one_bio(st
}
/* Must put everything in 512 byte sectors for the bio... */
- bio->bi_sector = (reg->hr_start_block + start_slot) << (bits - 9);
+ bio->bi_sector = (reg->hr_start_block + cs) << (bits - 9);
bio->bi_bdev = reg->hr_bdev;
bio->bi_private = wc;
bio->bi_end_io = o2hb_bio_end_io;
- first_page = start_slot / spp;
- last_page = first_page + nr_vecs;
- vec_start = (start_slot << bits) % PAGE_CACHE_SIZE;
- for(i = first_page; i < last_page; i++) {
- page = reg->hr_slot_data[i];
+ vec_start = (cs << bits) % PAGE_CACHE_SIZE;
+ while(cs < max_slots) {
+ current_page = cs / spp;
+ page = reg->hr_slot_data[current_page];
- vec_len = PAGE_CACHE_SIZE;
- /* last page might be short */
- if (((i + 1) * spp) > (start_slot + num_slots))
- vec_len = ((num_slots + start_slot) % spp) << bits;
- vec_len -= vec_start;
+ vec_len = min( PAGE_CACHE_SIZE,
+ (max_slots-cs) * (PAGE_CACHE_SIZE/spp) );
mlog(ML_HB_BIO, "page %d, vec_len = %u, vec_start = %u\n",
- i, vec_len, vec_start);
+ current_page, vec_len, vec_start);
len = bio_add_page(bio, page, vec_len, vec_start);
- if (len != vec_len) {
- bio_put(bio);
- bio = ERR_PTR(-EIO);
-
- mlog(ML_ERROR, "Error adding page to bio i = %d, "
- "vec_len = %u, len = %d\n, start = %u\n",
- i, vec_len, len, vec_start);
- goto bail;
- }
+ if (len != vec_len) break;
+ cs += vec_len / (PAGE_CACHE_SIZE/spp);
vec_start = 0;
}
bail:
+ *current_slot = cs;
return bio;
}
-/*
- * Compute the maximum number of sectors the bdev can handle in one bio,
- * as a power of two.
- *
- * Stolen from oracleasm, thanks Joel!
- */
-static int compute_max_sectors(struct block_device *bdev)
-{
- int max_pages, max_sectors, pow_two_sectors;
-
- struct request_queue *q;
-
- q = bdev_get_queue(bdev);
- max_pages = q->max_sectors >> (PAGE_SHIFT - 9);
- if (max_pages > BIO_MAX_PAGES)
- max_pages = BIO_MAX_PAGES;
- if (max_pages > q->max_phys_segments)
- max_pages = q->max_phys_segments;
- if (max_pages > q->max_hw_segments)
- max_pages = q->max_hw_segments;
- max_pages--; /* Handle I/Os that straddle a page */
-
- if (max_pages) {
- max_sectors = max_pages << (PAGE_SHIFT - 9);
- } else {
- /* If BIO contains 1 or less than 1 page. */
- max_sectors = q->max_sectors;
- }
- /* Why is fls() 1-based???? */
- pow_two_sectors = 1 << (fls(max_sectors) - 1);
-
- return pow_two_sectors;
-}
-
-static inline void o2hb_compute_request_limits(struct o2hb_region *reg,
- unsigned int num_slots,
- unsigned int *num_bios,
- unsigned int *slots_per_bio)
-{
- unsigned int max_sectors, io_sectors;
-
- max_sectors = compute_max_sectors(reg->hr_bdev);
-
- io_sectors = num_slots << (reg->hr_block_bits - 9);
-
- *num_bios = (io_sectors + max_sectors - 1) / max_sectors;
- *slots_per_bio = max_sectors >> (reg->hr_block_bits - 9);
-
- mlog(ML_HB_BIO, "My io size is %u sectors for %u slots. This "
- "device can handle %u sectors of I/O\n", io_sectors, num_slots,
- max_sectors);
- mlog(ML_HB_BIO, "Will need %u bios holding %u slots each\n",
- *num_bios, *slots_per_bio);
-}
-
static int o2hb_read_slots(struct o2hb_region *reg,
unsigned int max_slots)
{
- unsigned int num_bios, slots_per_bio, start_slot, num_slots;
- int i, status;
+ unsigned int current_slot=0;
+ int status;
struct o2hb_bio_wait_ctxt wc;
- struct bio **bios;
struct bio *bio;
- o2hb_compute_request_limits(reg, max_slots, &num_bios, &slots_per_bio);
+ o2hb_bio_wait_init(&wc);
- bios = kcalloc(num_bios, sizeof(struct bio *), GFP_KERNEL);
- if (!bios) {
- status = -ENOMEM;
- mlog_errno(status);
- return status;
- }
-
- o2hb_bio_wait_init(&wc, num_bios);
-
- num_slots = slots_per_bio;
- for(i = 0; i < num_bios; i++) {
- start_slot = i * slots_per_bio;
-
- /* adjust num_slots at last bio */
- if (max_slots < (start_slot + num_slots))
- num_slots = max_slots - start_slot;
-
- bio = o2hb_setup_one_bio(reg, &wc, start_slot, num_slots);
+ while(current_slot < max_slots) {
+ bio = o2hb_setup_one_bio(reg, &wc, ¤t_slot, max_slots);
if (IS_ERR(bio)) {
- o2hb_bio_wait_dec(&wc, num_bios - i);
-
status = PTR_ERR(bio);
mlog_errno(status);
goto bail_and_wait;
}
- bios[i] = bio;
+ atomic_inc(&wc.wc_num_reqs);
submit_bio(READ, bio);
}
@@ -403,38 +319,30 @@ bail_and_wait:
if (wc.wc_error && !status)
status = wc.wc_error;
- if (bios) {
- for(i = 0; i < num_bios; i++)
- if (bios[i])
- bio_put(bios[i]);
- kfree(bios);
- }
-
return status;
}
static int o2hb_issue_node_write(struct o2hb_region *reg,
- struct bio **write_bio,
struct o2hb_bio_wait_ctxt *write_wc)
{
int status;
unsigned int slot;
struct bio *bio;
- o2hb_bio_wait_init(write_wc, 1);
+ o2hb_bio_wait_init(write_wc);
slot = o2nm_this_node();
- bio = o2hb_setup_one_bio(reg, write_wc, slot, 1);
+ bio = o2hb_setup_one_bio(reg, write_wc, &slot, slot+1);
if (IS_ERR(bio)) {
status = PTR_ERR(bio);
mlog_errno(status);
goto bail;
}
+ atomic_inc(&write_wc->wc_num_reqs);
submit_bio(WRITE, bio);
- *write_bio = bio;
status = 0;
bail:
return status;
@@ -826,7 +734,6 @@ static int o2hb_do_disk_heartbeat(struct
{
int i, ret, highest_node, change = 0;
unsigned long configured_nodes[BITS_TO_LONGS(O2NM_MAX_NODES)];
- struct bio *write_bio;
struct o2hb_bio_wait_ctxt write_wc;
ret = o2nm_configured_node_map(configured_nodes,
@@ -864,7 +771,7 @@ static int o2hb_do_disk_heartbeat(struct
/* And fire off the write. Note that we don't wait on this I/O
* until later. */
- ret = o2hb_issue_node_write(reg, &write_bio, &write_wc);
+ ret = o2hb_issue_node_write(reg, &write_wc);
if (ret < 0) {
mlog_errno(ret);
return ret;
@@ -882,7 +789,6 @@ static int o2hb_do_disk_heartbeat(struct
* people we find in our steady state have seen us.
*/
o2hb_wait_on_io(reg, &write_wc);
- bio_put(write_bio);
if (write_wc.wc_error) {
/* Do not re-arm the write timeout on I/O error - we
* can't be sure that the new block ever made it to
@@ -943,7 +849,6 @@ static int o2hb_thread(void *data)
{
int i, ret;
struct o2hb_region *reg = data;
- struct bio *write_bio;
struct o2hb_bio_wait_ctxt write_wc;
struct timeval before_hb, after_hb;
unsigned int elapsed_msec;
@@ -993,10 +898,9 @@ static int o2hb_thread(void *data)
*
* XXX: Should we skip this on unclean_stop? */
o2hb_prepare_block(reg, 0);
- ret = o2hb_issue_node_write(reg, &write_bio, &write_wc);
+ ret = o2hb_issue_node_write(reg, &write_wc);
if (ret == 0) {
o2hb_wait_on_io(reg, &write_wc);
- bio_put(write_bio);
} else {
mlog_errno(ret);
}
--
: Dipl-Ing Philipp Reisner Tel +43-1-8178292-50 :
: LINBIT Information Technologies GmbH Fax +43-1-8178292-82 :
: Vivenotgasse 48, 1120 Vienna, Austria http://www.linbit.com :
More information about the drbd-dev
mailing list