[2.6.20.17 review 05/58] gen estimator deadlock fix

Willy Tarreau
2007-08-22T08:56:48Z

[-- Attachment #1: 0005-gen-estimator-deadlock-fix.patch --]
[-- Type: text/plain, Size: 5993 bytes --]

[NET]: gen_estimator deadlock fix

-Fixes ABBA deadlock noted by Patrick McHardy <kaber@trash.net>:

> There is at least one ABBA deadlock, est_timer() does:
> read_lock(&est_lock)
> spin_lock(e->stats_lock) (which is dev->queue_lock)
>
> and qdisc_destroy calls htb_destroy under dev->queue_lock, which
> calls htb_destroy_class, then gen_kill_estimator and this
> write_locks est_lock.

To fix the ABBA deadlock the rate estimators are now kept on an rcu list.

-The est_lock changes the use from protecting the list to protecting
the update to the 'bstat' pointer in order to avoid NULL dereferencing.

-The 'interval' member of the gen_estimator structure removed as it is
not needed.

Signed-off-by: Ranko Zivojnovic <ranko@spidernet.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
net/core/gen_estimator.c | 81 ++++++++++++++++++++++++++++------------------
1 files changed, 49 insertions(+), 32 deletions(-)

diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
index 33d82bf..acc1ee0 100644
--- a/net/core/gen_estimator.c
+++ b/net/core/gen_estimator.c
@@ -79,27 +79,27 @@

struct gen_estimator
{
- struct gen_estimator *next;
+ struct list_head list;
struct gnet_stats_basic *bstats;
struct gnet_stats_rate_est *rate_est;
spinlock_t *stats_lock;
- unsigned interval;
int ewma_log;
u64 last_bytes;
u32 last_packets;
u32 avpps;
u32 avbps;
+ struct rcu_head e_rcu;
};

struct gen_estimator_head
{
struct timer_list timer;
- struct gen_estimator *list;
+ struct list_head list;
};

static struct gen_estimator_head elist[EST_MAX_INTERVAL+1];

-/* Estimator array lock */
+/* Protects against NULL dereference */
static DEFINE_RWLOCK(est_lock);

static void est_timer(unsigned long arg)
@@ -107,13 +107,17 @@ static void est_timer(unsigned long arg)
int idx = (int)arg;
struct gen_estimator *e;

- read_lock(&est_lock);
- for (e = elist[idx].list; e; e = e->next) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(e, &elist[idx].list, list) {
u64 nbytes;
u32 npackets;
u32 rate;

spin_lock(e->stats_lock);
+ read_lock(&est_lock);
+ if (e->bstats == NULL)
+ goto skip;
+
nbytes = e->bstats->bytes;
npackets = e->bstats->packets;
rate = (nbytes - e->last_bytes)<<(7 - idx);
@@ -125,12 +129,14 @@ static void est_timer(unsigned long arg)
e->last_packets = npackets;
e->avpps += ((long)rate - (long)e->avpps) >> e->ewma_log;
e->rate_est->pps = (e->avpps+0x1FF)>>10;
+skip:
+ read_unlock(&est_lock);
spin_unlock(e->stats_lock);
}

- if (elist[idx].list != NULL)
+ if (!list_empty(&elist[idx].list))
mod_timer(&elist[idx].timer, jiffies + ((HZ<<idx)/4));
- read_unlock(&est_lock);
+ rcu_read_unlock();
}

/**
@@ -147,12 +153,17 @@ static void est_timer(unsigned long arg)
* &rate_est with the statistics lock grabed during this period.
*
* Returns 0 on success or a negative error code.
+ *
+ * NOTE: Called under rtnl_mutex
*/
int gen_new_estimator(struct gnet_stats_basic *bstats,
- struct gnet_stats_rate_est *rate_est, spinlock_t *stats_lock, struct rtattr *opt)
+ struct gnet_stats_rate_est *rate_est,
+ spinlock_t *stats_lock,
+ struct rtattr *opt)
{
struct gen_estimator *est;
struct gnet_estimator *parm = RTA_DATA(opt);
+ int idx;

if (RTA_PAYLOAD(opt) < sizeof(*parm))
return -EINVAL;
@@ -164,7 +175,7 @@ int gen_new_estimator(struct gnet_stats_basic *bstats,
if (est == NULL)
return -ENOBUFS;

- est->interval = parm->interval + 2;
+ idx = parm->interval + 2;
est->bstats = bstats;
est->rate_est = rate_est;
est->stats_lock = stats_lock;
@@ -174,20 +185,25 @@ int gen_new_estimator(struct gnet_stats_basic *bstats,
est->last_packets = bstats->packets;
est->avpps = rate_est->pps<<10;

- est->next = elist[est->interval].list;
- if (est->next == NULL) {
- init_timer(&elist[est->interval].timer);
- elist[est->interval].timer.data = est->interval;
- elist[est->interval].timer.expires = jiffies + ((HZ<<est->interval)/4);
- elist[est->interval].timer.function = est_timer;
- add_timer(&elist[est->interval].timer);
+ if (!elist[idx].timer.function) {
+ INIT_LIST_HEAD(&elist[idx].list);
+ setup_timer(&elist[idx].timer, est_timer, idx);
}
- write_lock_bh(&est_lock);
- elist[est->interval].list = est;
- write_unlock_bh(&est_lock);
+
+ if (list_empty(&elist[idx].list))
+ mod_timer(&elist[idx].timer, jiffies + ((HZ<<idx)/4));
+
+ list_add_rcu(&est->list, &elist[idx].list);
return 0;
}

+static void __gen_kill_estimator(struct rcu_head *head)
+{
+ struct gen_estimator *e = container_of(head,
+ struct gen_estimator, e_rcu);
+ kfree(e);
+}
+
/**
* gen_kill_estimator - remove a rate estimator
* @bstats: basic statistics
@@ -195,31 +211,32 @@ int gen_new_estimator(struct gnet_stats_basic *bstats,
*
* Removes the rate estimator specified by &bstats and &rate_est
* and deletes the timer.
+ *
+ * NOTE: Called under rtnl_mutex
*/
void gen_kill_estimator(struct gnet_stats_basic *bstats,
struct gnet_stats_rate_est *rate_est)
{
int idx;
- struct gen_estimator *est, **pest;
+ struct gen_estimator *e, *n;

for (idx=0; idx <= EST_MAX_INTERVAL; idx++) {
- int killed = 0;
- pest = &elist[idx].list;
- while ((est=*pest) != NULL) {
- if (est->rate_est != rate_est || est->bstats != bstats) {
- pest = &est->next;
+
+ /* Skip non initialized indexes */
+ if (!elist[idx].timer.function)
+ continue;
+
+ list_for_each_entry_safe(e, n, &elist[idx].list, list) {
+ if (e->rate_est != rate_est || e->bstats != bstats)
continue;
- }

write_lock_bh(&est_lock);
- *pest = est->next;
+ e->bstats = NULL;
write_unlock_bh(&est_lock);

- kfree(est);
- killed++;
+ list_del_rcu(&e->list);
+ call_rcu(&e->e_rcu, __gen_kill_estimator);
}
- if (killed && elist[idx].list == NULL)
- del_timer(&elist[idx].timer);
}
}

--
1.5.2.5

--