[PATCH net-next] net: dst_cache: annotate data-races around dst_cache->reset_ts

[PATCH net-next] net: dst_cache: annotate data-races around dst_cache->reset_ts

[Eric Dumazet]

dst_cache->reset_ts is read or written locklessly,
add READ_ONCE() and WRITE_ONCE() annotations.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/dst_cache.h | 2 +-
 net/core/dst_cache.c    | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/net/dst_cache.h b/include/net/dst_cache.h
index df6622a5fe98f0a9732617bb2a757ef9c9611797..b4a55d2d5e71b974b0012bc7ec9a5970a6c0dffe 100644
--- a/include/net/dst_cache.h
+++ b/include/net/dst_cache.h
@@ -76,7 +76,7 @@ struct dst_entry *dst_cache_get_ip6(struct dst_cache *dst_cache,
  */
 static inline void dst_cache_reset(struct dst_cache *dst_cache)
 {
-	dst_cache->reset_ts = jiffies;
+	WRITE_ONCE(dst_cache->reset_ts, jiffies);
 }
 
 /**
diff --git a/net/core/dst_cache.c b/net/core/dst_cache.c
index 0c0bdb058c5b1ab81e14aa48d8612a6253a7c852..f9df84a6c4b2dbe63c6f61fb431e179f92e072e0 100644
--- a/net/core/dst_cache.c
+++ b/net/core/dst_cache.c
@@ -47,7 +47,8 @@ static struct dst_entry *dst_cache_per_cpu_get(struct dst_cache *dst_cache,
 	/* the cache already hold a dst reference; it can't go away */
 	dst_hold(dst);
 
-	if (unlikely(!time_after(idst->refresh_ts, dst_cache->reset_ts) ||
+	if (unlikely(!time_after(idst->refresh_ts,
+				 READ_ONCE(dst_cache->reset_ts)) ||
 		     (dst->obsolete && !dst->ops->check(dst, idst->cookie)))) {
 		dst_cache_per_cpu_dst_set(idst, NULL, 0);
 		dst_release(dst);
@@ -170,7 +171,7 @@ void dst_cache_reset_now(struct dst_cache *dst_cache)
 	if (!dst_cache->cache)
 		return;
 
-	dst_cache->reset_ts = jiffies;
+	dst_cache_reset(dst_cache);
 	for_each_possible_cpu(i) {
 		struct dst_cache_pcpu *idst = per_cpu_ptr(dst_cache->cache, i);
 		struct dst_entry *dst = idst->dst;
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog

Re: [PATCH net-next] net: dst_cache: annotate data-races around dst_cache->reset_ts

[Paolo Abeni]

On Tue, 2024-05-07 at 13:20 +0000, Eric Dumazet wrote:
> dst_cache->reset_ts is read or written locklessly,
> add READ_ONCE() and WRITE_ONCE() annotations.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

I was wondering if we need the annotation when the RD/WR ops all happen
on the same CPU, but dst_cache_reset() can happen on a different core,
so LGTM, thanks!

Acked-by: Paolo Abeni <pabeni@redhat.com>

Re: [PATCH net-next] net: dst_cache: annotate data-races around dst_cache->reset_ts

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue,  7 May 2024 13:20:00 +0000 you wrote:
> dst_cache->reset_ts is read or written locklessly,
> add READ_ONCE() and WRITE_ONCE() annotations.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
>  include/net/dst_cache.h | 2 +-
>  net/core/dst_cache.c    | 5 +++--
>  2 files changed, 4 insertions(+), 3 deletions(-)

Here is the summary with links:
  - [net-next] net: dst_cache: annotate data-races around dst_cache->reset_ts
    https://git.kernel.org/netdev/net-next/c/3b09b2bd0d62

You are awesome, thank you!
-- 
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