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md/raid5: don't complete make_request on barrier until writes are scheduled 

The post-barrier-flush is sent by md as soon as make_request on the
barrier write completes.  For raid5, the data might not be in the
per-device queues yet.  So for barrier requests, wait for any
pre-reading to be done so that the request will be in the per-device
queues.

We use the 'preread_active' count to check that nothing is still in
the preread phase, and delay the decrement of this count until after
write requests have been submitted to the underlying devices.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2009-12-14 12:49:50 +11:00
parent a2826aa92e
commit 729a18663a
1 changed files with 39 additions and 12 deletions
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51
drivers/md/raid5.c
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@ -2947,6 +2947,7 @@ static void handle_stripe5(struct stripe_head *sh)
struct r5dev *dev;
mdk_rdev_t *blocked_rdev = NULL;
int prexor;
int dec_preread_active = 0;
memset(&s, 0, sizeof(s));
pr_debug("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d check:%d "
@ -3096,12 +3097,8 @@ static void handle_stripe5(struct stripe_head *sh)
set_bit(STRIPE_INSYNC, &sh->state);
}
}
if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
atomic_dec(&conf->preread_active_stripes);
if (atomic_read(&conf->preread_active_stripes) <
IO_THRESHOLD)
md_wakeup_thread(conf->mddev->thread);
}
if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
dec_preread_active = 1;
}
/* Now to consider new write requests and what else, if anything
@ -3208,6 +3205,16 @@ static void handle_stripe5(struct stripe_head *sh)
ops_run_io(sh, &s);
if (dec_preread_active) {
/* We delay this until after ops_run_io so that if make_request
* is waiting on a barrier, it won't continue until the writes
* have actually been submitted.
*/
atomic_dec(&conf->preread_active_stripes);
if (atomic_read(&conf->preread_active_stripes) <
IO_THRESHOLD)
md_wakeup_thread(conf->mddev->thread);
}
return_io(return_bi);
}
@ -3221,6 +3228,7 @@ static void handle_stripe6(struct stripe_head *sh)
struct r6_state r6s;
struct r5dev *dev, *pdev, *qdev;
mdk_rdev_t *blocked_rdev = NULL;
int dec_preread_active = 0;
pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
"pd_idx=%d, qd_idx=%d\n, check:%d, reconstruct:%d\n",
@ -3379,12 +3387,8 @@ static void handle_stripe6(struct stripe_head *sh)
set_bit(STRIPE_INSYNC, &sh->state);
}
}
if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
atomic_dec(&conf->preread_active_stripes);
if (atomic_read(&conf->preread_active_stripes) <
IO_THRESHOLD)
md_wakeup_thread(conf->mddev->thread);
}
if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
dec_preread_active = 1;
}
/* Now to consider new write requests and what else, if anything
@ -3493,6 +3497,18 @@ static void handle_stripe6(struct stripe_head *sh)
ops_run_io(sh, &s);
if (dec_preread_active) {
/* We delay this until after ops_run_io so that if make_request
* is waiting on a barrier, it won't continue until the writes
* have actually been submitted.
*/
atomic_dec(&conf->preread_active_stripes);
if (atomic_read(&conf->preread_active_stripes) <
IO_THRESHOLD)
md_wakeup_thread(conf->mddev->thread);
}
return_io(return_bi);
}
@ -3995,6 +4011,9 @@ static int make_request(struct request_queue *q, struct bio * bi)
finish_wait(&conf->wait_for_overlap, &w);
set_bit(STRIPE_HANDLE, &sh->state);
clear_bit(STRIPE_DELAYED, &sh->state);
if (mddev->barrier &&
!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
atomic_inc(&conf->preread_active_stripes);
release_stripe(sh);
} else {
/* cannot get stripe for read-ahead, just give-up */
@ -4014,6 +4033,14 @@ static int make_request(struct request_queue *q, struct bio * bi)
bio_endio(bi, 0);
}
if (mddev->barrier) {
/* We need to wait for the stripes to all be handled.
* So: wait for preread_active_stripes to drop to 0.
*/
wait_event(mddev->thread->wqueue,
atomic_read(&conf->preread_active_stripes) == 0);
}
return 0;
}