diff options
| author | Eric Dumazet | 2022-05-15 21:24:53 -0700 |
|---|---|---|
| committer | David S. Miller | 2022-05-16 11:33:59 +0100 |
| commit | 97e719a82b43c6c2bb5eebdb3c5d479a332ac2ac (patch) | |
| tree | 7e38c6a88703169d84365cb91c9aaab5aabe0adb | |
| parent | 3daebfbeb4555cb0c113aeb88aa469192ee41d89 (diff) | |
net: fix possible race in skb_attempt_defer_free()
A cpu can observe sd->defer_count reaching 128,
and call smp_call_function_single_async()
Problem is that the remote CPU can clear sd->defer_count
before the IPI is run/acknowledged.
Other cpus can queue more packets and also decide
to call smp_call_function_single_async() while the pending
IPI was not yet delivered.
This is a common issue with smp_call_function_single_async().
Callers must ensure correct synchronization and serialization.
I triggered this issue while experimenting smaller threshold.
Performing the call to smp_call_function_single_async()
under sd->defer_lock protection did not solve the problem.
Commit 5a18ceca6350 ("smp: Allow smp_call_function_single_async()
to insert locked csd") replaced an informative WARN_ON_ONCE()
with a return of -EBUSY, which is often ignored.
Test of CSD_FLAG_LOCK presence is racy anyway.
Fixes: 68822bdf76f1 ("net: generalize skb freeing deferral to per-cpu lists")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | include/linux/netdevice.h | 1 | ||||
| -rw-r--r-- | net/core/dev.c | 7 | ||||
| -rw-r--r-- | net/core/skbuff.c | 5 |
3 files changed, 8 insertions, 5 deletions
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index d57ce248004c..cbaf312e365b 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -3136,6 +3136,7 @@ struct softnet_data { /* Another possibly contended cache line */ spinlock_t defer_lock ____cacheline_aligned_in_smp; int defer_count; + int defer_ipi_scheduled; struct sk_buff *defer_list; call_single_data_t defer_csd; }; diff --git a/net/core/dev.c b/net/core/dev.c index d93456c75b55..a5e663e1a75a 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4582,9 +4582,12 @@ static void rps_trigger_softirq(void *data) #endif /* CONFIG_RPS */ /* Called from hardirq (IPI) context */ -static void trigger_rx_softirq(void *data __always_unused) +static void trigger_rx_softirq(void *data) { + struct softnet_data *sd = data; + __raise_softirq_irqoff(NET_RX_SOFTIRQ); + smp_store_release(&sd->defer_ipi_scheduled, 0); } /* @@ -11382,7 +11385,7 @@ static int __init net_dev_init(void) INIT_CSD(&sd->csd, rps_trigger_softirq, sd); sd->cpu = i; #endif - INIT_CSD(&sd->defer_csd, trigger_rx_softirq, NULL); + INIT_CSD(&sd->defer_csd, trigger_rx_softirq, sd); spin_lock_init(&sd->defer_lock); init_gro_hash(&sd->backlog); diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 2fea964f09d8..b40c8cdf4785 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6516,8 +6516,7 @@ void skb_attempt_defer_free(struct sk_buff *skb) sd->defer_count++; /* kick every time queue length reaches 128. - * This should avoid blocking in smp_call_function_single_async(). - * This condition should hardly be bit under normal conditions, + * This condition should hardly be hit under normal conditions, * unless cpu suddenly stopped to receive NIC interrupts. */ kick = sd->defer_count == 128; @@ -6527,6 +6526,6 @@ void skb_attempt_defer_free(struct sk_buff *skb) /* Make sure to trigger NET_RX_SOFTIRQ on the remote CPU * if we are unlucky enough (this seems very unlikely). */ - if (unlikely(kick)) + if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1)) smp_call_function_single_async(cpu, &sd->defer_csd); } |