NeilBrown <neilb@xxxxxxx> writes:
> sh->lock is now mainly used to ensure that two threads aren't running
> in the locked part of handle_stripe[56] at the same time.
>
> That can more neatly be achieved with an 'active' flag which we set
> while running handle_stripe. If we find the flag is set, we simply
> requeue the stripe for later by setting STRIPE_HANDLE.
>
> For safety we take ->device_lock while examining the state of the
> stripe and creating a summary in 'stripe_head_state / r6_state'.
> This possibly isn't needed but as shared fields like ->toread,
> ->towrite are checked it is safer for now at least.
>
> We leave the label after the old 'unlock' called "unlock" because it
> will disappear in a few patches, so renaming seems pointless.
>
> This leaves the stripe 'locked' for longer as we clear STRIPE_ACTIVE
> later, but that is not a problem.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxx>
But I have a question, please see below.
> ---
>
> drivers/md/raid5.c | 26 +++++++++++++-------------
> drivers/md/raid5.h | 2 +-
> 2 files changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 9985138..f8275b5 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -1020,14 +1020,12 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
> if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
> struct bio *wbi;
>
> - spin_lock(&sh->lock);
> spin_lock_irq(&sh->raid_conf->device_lock);
> chosen = dev->towrite;
> dev->towrite = NULL;
> BUG_ON(dev->written);
> wbi = dev->written = chosen;
> spin_unlock_irq(&sh->raid_conf->device_lock);
> - spin_unlock(&sh->lock);
>
> while (wbi && wbi->bi_sector <
> dev->sector + STRIPE_SECTORS) {
> @@ -1322,7 +1320,6 @@ static int grow_one_stripe(raid5_conf_t *conf)
> return 0;
>
> sh->raid_conf = conf;
> - spin_lock_init(&sh->lock);
> #ifdef CONFIG_MULTICORE_RAID456
> init_waitqueue_head(&sh->ops.wait_for_ops);
> #endif
> @@ -1442,7 +1439,6 @@ static int resize_stripes(raid5_conf_t *conf, int newsize)
> break;
>
> nsh->raid_conf = conf;
> - spin_lock_init(&nsh->lock);
> #ifdef CONFIG_MULTICORE_RAID456
> init_waitqueue_head(&nsh->ops.wait_for_ops);
> #endif
> @@ -2148,7 +2144,6 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
> (unsigned long long)sh->sector);
>
>
> - spin_lock(&sh->lock);
> spin_lock_irq(&conf->device_lock);
> if (forwrite) {
> bip = &sh->dev[dd_idx].towrite;
> @@ -2184,7 +2179,6 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
> set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
> }
> spin_unlock_irq(&conf->device_lock);
> - spin_unlock(&sh->lock);
>
> pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
> (unsigned long long)(*bip)->bi_sector,
> @@ -2201,7 +2195,6 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
> overlap:
> set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
> spin_unlock_irq(&conf->device_lock);
> - spin_unlock(&sh->lock);
> return 0;
> }
>
> @@ -3023,12 +3016,10 @@ static void handle_stripe5(struct stripe_head *sh)
> atomic_read(&sh->count), sh->pd_idx, sh->check_state,
> sh->reconstruct_state);
>
> - spin_lock(&sh->lock);
> if (test_and_clear_bit(STRIPE_SYNC_REQUESTED, &sh->state)) {
> set_bit(STRIPE_SYNCING, &sh->state);
> clear_bit(STRIPE_INSYNC, &sh->state);
> }
> - clear_bit(STRIPE_HANDLE, &sh->state);
> clear_bit(STRIPE_DELAYED, &sh->state);
>
> s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
> @@ -3037,6 +3028,7 @@ static void handle_stripe5(struct stripe_head *sh)
>
> /* Now to look around and see what can be done */
> rcu_read_lock();
> + spin_lock_irq(&conf->device_lock);
Do we still need rcu_read_lock()? AFAIK rcu_read_lock() only prevents
task from preemption but spin_lock does same thing as well.
I know it's been already there under sh->lock before this patch, and
it doesn't hurt anything, but I'm not sure it is really needed.
> for (i=disks; i--; ) {
> mdk_rdev_t *rdev;
>
> @@ -3099,6 +3091,7 @@ static void handle_stripe5(struct stripe_head *sh)
> s.failed_num = i;
> }
> }
> + spin_unlock_irq(&conf->device_lock);
> rcu_read_unlock();
>
> if (unlikely(blocked_rdev)) {
> @@ -3275,7 +3268,6 @@ static void handle_stripe5(struct stripe_head *sh)
> handle_stripe_expansion(conf, sh, NULL);
>
> unlock:
> - spin_unlock(&sh->lock);
>
> /* wait for this device to become unblocked */
> if (unlikely(blocked_rdev))
> @@ -3318,12 +3310,10 @@ static void handle_stripe6(struct stripe_head *sh)
> sh->check_state, sh->reconstruct_state);
> memset(&s, 0, sizeof(s));
>
> - spin_lock(&sh->lock);
> if (test_and_clear_bit(STRIPE_SYNC_REQUESTED, &sh->state)) {
> set_bit(STRIPE_SYNCING, &sh->state);
> clear_bit(STRIPE_INSYNC, &sh->state);
> }
> - clear_bit(STRIPE_HANDLE, &sh->state);
> clear_bit(STRIPE_DELAYED, &sh->state);
>
> s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
> @@ -3332,6 +3322,7 @@ static void handle_stripe6(struct stripe_head *sh)
> /* Now to look around and see what can be done */
>
> rcu_read_lock();
> + spin_lock_irq(&conf->device_lock);
Same here.
> for (i=disks; i--; ) {
> mdk_rdev_t *rdev;
> dev = &sh->dev[i];
> @@ -3395,6 +3386,7 @@ static void handle_stripe6(struct stripe_head *sh)
> s.failed++;
> }
> }
> + spin_unlock_irq(&conf->device_lock);
> rcu_read_unlock();
>
> if (unlikely(blocked_rdev)) {
> @@ -3580,7 +3572,6 @@ static void handle_stripe6(struct stripe_head *sh)
> handle_stripe_expansion(conf, sh, &r6s);
>
> unlock:
> - spin_unlock(&sh->lock);
>
> /* wait for this device to become unblocked */
> if (unlikely(blocked_rdev))
> @@ -3608,10 +3599,19 @@ static void handle_stripe6(struct stripe_head *sh)
>
> static void handle_stripe(struct stripe_head *sh)
> {
> + clear_bit(STRIPE_HANDLE, &sh->state);
> + if (test_and_set_bit(STRIPE_ACTIVE, &sh->state)) {
> + /* already being handled, ensure it gets handled
> + * again when current action finishes */
> + set_bit(STRIPE_HANDLE, &sh->state);
> + return;
> + }
> +
> if (sh->raid_conf->level == 6)
> handle_stripe6(sh);
> else
> handle_stripe5(sh);
> + clear_bit(STRIPE_ACTIVE, &sh->state);
> }
>
> static void raid5_activate_delayed(raid5_conf_t *conf)
> diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
> index a330011..217a9d4 100644
> --- a/drivers/md/raid5.h
> +++ b/drivers/md/raid5.h
> @@ -209,7 +209,6 @@ struct stripe_head {
> short ddf_layout;/* use DDF ordering to calculate Q */
> unsigned long state; /* state flags */
> atomic_t count; /* nr of active thread/requests */
> - spinlock_t lock;
> int bm_seq; /* sequence number for bitmap flushes */
> int disks; /* disks in stripe */
> enum check_states check_state;
> @@ -290,6 +289,7 @@ struct r6_state {
> * Stripe state
> */
> enum {
> + STRIPE_ACTIVE,
> STRIPE_HANDLE,
> STRIPE_SYNC_REQUESTED,
> STRIPE_SYNCING,
>
>
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