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Subject[PATCH 10/15] drbd: RCU for rs_plan_s
Date
This removes the issue with using peer_seq_lock out of different
contexts.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
---
drivers/block/drbd/drbd_int.h | 2 +-
drivers/block/drbd/drbd_nl.c | 18 +++++++--------
drivers/block/drbd/drbd_receiver.c | 17 +++++++--------
drivers/block/drbd/drbd_worker.c | 41 +++++++++++++++++++++---------------
4 files changed, 41 insertions(+), 37 deletions(-)
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 2ecee6c..3f377e2 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -998,7 +998,7 @@ struct drbd_conf {
int rs_last_events; /* counter of read or write "events" (unit sectors)
* on the lower level device when we last looked. */
int c_sync_rate; /* current resync rate after syncer throttle magic */
- struct fifo_buffer *rs_plan_s; /* correction values of resync planer */
+ struct fifo_buffer *rs_plan_s; /* correction values of resync planer (RCU, tconn->conn_update) */
int rs_in_flight; /* resync sectors in flight (to proxy, in proxy and from proxy) */
atomic_t ap_in_flight; /* App sectors in flight (waiting for ack) */
int peer_max_bio_size;
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 6d05bf5..ca39deb 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1137,7 +1137,7 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
enum drbd_ret_code retcode;
struct drbd_conf *mdev;
struct disk_conf *new_disk_conf, *old_disk_conf;
- struct fifo_buffer *rs_plan_s = NULL;
+ struct fifo_buffer *old_plan = NULL, *new_plan = NULL;
int err, fifo_size;

retcode = drbd_adm_prepare(skb, info, DRBD_ADM_NEED_MINOR);
@@ -1194,8 +1194,8 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)

fifo_size = (new_disk_conf->c_plan_ahead * 10 * SLEEP_TIME) / HZ;
if (fifo_size != mdev->rs_plan_s->size) {
- rs_plan_s = fifo_alloc(fifo_size);
- if (!rs_plan_s) {
+ new_plan = fifo_alloc(fifo_size);
+ if (!new_plan) {
dev_err(DEV, "kmalloc of fifo_buffer failed");
retcode = ERR_NOMEM;
goto fail_unlock;
@@ -1224,13 +1224,10 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
if (retcode != NO_ERROR)
goto fail_unlock;

- spin_lock(&mdev->peer_seq_lock);
- if (rs_plan_s) {
- kfree(mdev->rs_plan_s);
- mdev->rs_plan_s = rs_plan_s;
- rs_plan_s = NULL;
+ if (new_plan) {
+ old_plan = mdev->rs_plan_s;
+ rcu_assign_pointer(mdev->rs_plan_s, new_plan);
}
- spin_unlock(&mdev->peer_seq_lock);

drbd_md_sync(mdev);

@@ -1240,13 +1237,14 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
mutex_unlock(&mdev->tconn->conf_update);
synchronize_rcu();
kfree(old_disk_conf);
+ kfree(old_plan);
goto success;

fail_unlock:
mutex_unlock(&mdev->tconn->conf_update);
fail:
kfree(new_disk_conf);
- kfree(rs_plan_s);
+ kfree(new_plan);
success:
put_ldev(mdev);
out:
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 19b421f..73f605b 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3159,7 +3159,7 @@ static int receive_SyncParam(struct drbd_tconn *tconn, struct packet_info *pi)
struct net_conf *old_net_conf, *new_net_conf = NULL;
struct disk_conf *old_disk_conf, *new_disk_conf = NULL;
const int apv = tconn->agreed_pro_version;
- struct fifo_buffer *rs_plan_s = NULL;
+ struct fifo_buffer *old_plan = NULL, *new_plan = NULL;
int fifo_size = 0;
int err;

@@ -3278,8 +3278,8 @@ static int receive_SyncParam(struct drbd_tconn *tconn, struct packet_info *pi)

fifo_size = (new_disk_conf->c_plan_ahead * 10 * SLEEP_TIME) / HZ;
if (fifo_size != mdev->rs_plan_s->size) {
- rs_plan_s = fifo_alloc(fifo_size);
- if (!rs_plan_s) {
+ new_plan = fifo_alloc(fifo_size);
+ if (!new_plan) {
dev_err(DEV, "kmalloc of fifo_buffer failed");
put_ldev(mdev);
goto disconnect;
@@ -3315,23 +3315,22 @@ static int receive_SyncParam(struct drbd_tconn *tconn, struct packet_info *pi)
}

rcu_assign_pointer(mdev->ldev->disk_conf, new_disk_conf);
- spin_lock(&mdev->peer_seq_lock);
- if (rs_plan_s) {
- kfree(mdev->rs_plan_s);
- mdev->rs_plan_s = rs_plan_s;
+ if (new_plan) {
+ old_plan = mdev->rs_plan_s;
+ rcu_assign_pointer(mdev->rs_plan_s, new_plan);
}
- spin_unlock(&mdev->peer_seq_lock);

mutex_unlock(&mdev->tconn->conf_update);
synchronize_rcu();
if (new_net_conf)
kfree(old_net_conf);
kfree(old_disk_conf);
+ kfree(old_plan);

return 0;

disconnect:
- kfree(rs_plan_s);
+ kfree(new_plan);
mutex_unlock(&mdev->tconn->conf_update);
/* just for completeness: actually not needed,
* as this is not reached if csums_tfm was ok. */
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 866924f..484a08b 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -460,15 +460,15 @@ static int drbd_rs_controller(struct drbd_conf *mdev)
int steps; /* Number of time steps to plan ahead */
int curr_corr;
int max_sect;
+ struct fifo_buffer *plan;

sect_in = atomic_xchg(&mdev->rs_sect_in, 0); /* Number of sectors that came in */
mdev->rs_in_flight -= sect_in;

- spin_lock(&mdev->peer_seq_lock); /* get an atomic view on mdev->rs_plan_s */
- rcu_read_lock();
dc = rcu_dereference(mdev->ldev->disk_conf);
+ plan = rcu_dereference(mdev->rs_plan_s);

- steps = mdev->rs_plan_s->size; /* (dc->c_plan_ahead * 10 * SLEEP_TIME) / HZ; */
+ steps = plan->size; /* (dc->c_plan_ahead * 10 * SLEEP_TIME) / HZ; */

if (mdev->rs_in_flight + sect_in == 0) { /* At start of resync */
want = ((dc->resync_rate * 2 * SLEEP_TIME) / HZ) * steps;
@@ -477,16 +477,16 @@ static int drbd_rs_controller(struct drbd_conf *mdev)
sect_in * dc->c_delay_target * HZ / (SLEEP_TIME * 10);
}

- correction = want - mdev->rs_in_flight - mdev->rs_plan_s->total;
+ correction = want - mdev->rs_in_flight - plan->total;

/* Plan ahead */
cps = correction / steps;
- fifo_add_val(mdev->rs_plan_s, cps);
- mdev->rs_plan_s->total += cps * steps;
+ fifo_add_val(plan, cps);
+ plan->total += cps * steps;

/* What we do in this step */
- curr_corr = fifo_push(mdev->rs_plan_s, 0);
- mdev->rs_plan_s->total -= curr_corr;
+ curr_corr = fifo_push(plan, 0);
+ plan->total -= curr_corr;

req_sect = sect_in + curr_corr;
if (req_sect < 0)
@@ -501,8 +501,6 @@ static int drbd_rs_controller(struct drbd_conf *mdev)
sect_in, mdev->rs_in_flight, want, correction,
steps, cps, mdev->rs_planed, curr_corr, req_sect);
*/
- rcu_read_unlock();
- spin_unlock(&mdev->peer_seq_lock);

return req_sect;
}
@@ -510,15 +508,16 @@ static int drbd_rs_controller(struct drbd_conf *mdev)
static int drbd_rs_number_requests(struct drbd_conf *mdev)
{
int number;
- if (mdev->rs_plan_s->size) { /* rcu_dereference(mdev->ldev->disk_conf)->c_plan_ahead */
+
+ rcu_read_lock();
+ if (rcu_dereference(mdev->rs_plan_s)->size) {
number = drbd_rs_controller(mdev) >> (BM_BLOCK_SHIFT - 9);
mdev->c_sync_rate = number * HZ * (BM_BLOCK_SIZE / 1024) / SLEEP_TIME;
} else {
- rcu_read_lock();
mdev->c_sync_rate = rcu_dereference(mdev->ldev->disk_conf)->resync_rate;
- rcu_read_unlock();
number = SLEEP_TIME * mdev->c_sync_rate / ((BM_BLOCK_SIZE / 1024) * HZ);
}
+ rcu_read_unlock();

/* ignore the amount of pending requests, the resync controller should
* throttle down to incoming reply rate soon enough anyways. */
@@ -1468,13 +1467,21 @@ void drbd_sync_after_changed(struct drbd_conf *mdev)

void drbd_rs_controller_reset(struct drbd_conf *mdev)
{
+ struct fifo_buffer *plan;
+
atomic_set(&mdev->rs_sect_in, 0);
atomic_set(&mdev->rs_sect_ev, 0);
mdev->rs_in_flight = 0;
- mdev->rs_plan_s->total = 0;
- spin_lock(&mdev->peer_seq_lock);
- fifo_set(mdev->rs_plan_s, 0);
- spin_unlock(&mdev->peer_seq_lock);
+
+ /* Updating the RCU protected object in place is necessary since
+ this function gets called from atomic context.
+ It is valid since all other updates also lead to an completely
+ empty fifo */
+ rcu_read_lock();
+ plan = rcu_dereference(mdev->rs_plan_s);
+ plan->total = 0;
+ fifo_set(plan, 0);
+ rcu_read_unlock();
}

void start_resync_timer_fn(unsigned long data)
--
1.7.4.1


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