[PATCH net] sock: annotate data-races around prot->memory_pressure

[PATCH net] sock: annotate data-races around prot->memory_pressure

[Eric Dumazet]

*prot->memory_pressure is read/writen locklessly, we need
to add proper annotations.

A recent commit added a new race, it is time to audit all accesses.

Fixes: 2d0c88e84e48 ("sock: Fix misuse of sk_under_memory_pressure()")
Fixes: 4d93df0abd50 ("[SCTP]: Rewrite of sctp buffer management code")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Abel Wu <wuyun.abel@bytedance.com>
Cc: Shakeel Butt <shakeelb@google.com>
---
 include/net/sock.h | 7 ++++---
 net/sctp/socket.c  | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index e3d987b2ef124024110a0c67c4c4775742d3eb2d..690e22139543fb6eaf3ccd08475d2c6934231dbf 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1323,6 +1323,7 @@ struct proto {
 	/*
 	 * Pressure flag: try to collapse.
 	 * Technical note: it is used by multiple contexts non atomically.
+	 * Make sure to use READ_ONCE()/WRITE_ONCE() for all reads/writes.
 	 * All the __sk_mem_schedule() is of this nature: accounting
 	 * is strict, actions are advisory and have some latency.
 	 */
@@ -1423,7 +1424,7 @@ static inline bool sk_has_memory_pressure(const struct sock *sk)
 static inline bool sk_under_global_memory_pressure(const struct sock *sk)
 {
 	return sk->sk_prot->memory_pressure &&
-		!!*sk->sk_prot->memory_pressure;
+		!!READ_ONCE(*sk->sk_prot->memory_pressure);
 }
 
 static inline bool sk_under_memory_pressure(const struct sock *sk)
@@ -1435,7 +1436,7 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
 	    mem_cgroup_under_socket_pressure(sk->sk_memcg))
 		return true;
 
-	return !!*sk->sk_prot->memory_pressure;
+	return !!READ_ONCE(*sk->sk_prot->memory_pressure);
 }
 
 static inline long
@@ -1512,7 +1513,7 @@ proto_memory_pressure(struct proto *prot)
 {
 	if (!prot->memory_pressure)
 		return false;
-	return !!*prot->memory_pressure;
+	return !!READ_ONCE(*prot->memory_pressure);
 }
 
 
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 9388d98aebc033f195e56d5295fd998996d41f7e..6da738f60f4b534d12245455c39bf4db18d8cb5a 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -99,7 +99,7 @@ struct percpu_counter sctp_sockets_allocated;
 
 static void sctp_enter_memory_pressure(struct sock *sk)
 {
-	sctp_memory_pressure = 1;
+	WRITE_ONCE(sctp_memory_pressure, 1);
 }
 
 
-- 
2.42.0.rc1.204.g551eb34607-goog

Re: [PATCH net] sock: annotate data-races around prot->memory_pressure

[Shakeel Butt]

On Thu, Aug 17, 2023 at 6:51 PM Eric Dumazet <edumazet@google.com> wrote:
>
> *prot->memory_pressure is read/writen locklessly, we need
> to add proper annotations.
>
> A recent commit added a new race, it is time to audit all accesses.
>
> Fixes: 2d0c88e84e48 ("sock: Fix misuse of sk_under_memory_pressure()")
> Fixes: 4d93df0abd50 ("[SCTP]: Rewrite of sctp buffer management code")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Abel Wu <wuyun.abel@bytedance.com>
> Cc: Shakeel Butt <shakeelb@google.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH net] sock: annotate data-races around prot->memory_pressure

[patchwork-bot+netdevbpf]

Hello:

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

On Fri, 18 Aug 2023 01:51:32 +0000 you wrote:
> *prot->memory_pressure is read/writen locklessly, we need
> to add proper annotations.
> 
> A recent commit added a new race, it is time to audit all accesses.
> 
> Fixes: 2d0c88e84e48 ("sock: Fix misuse of sk_under_memory_pressure()")
> Fixes: 4d93df0abd50 ("[SCTP]: Rewrite of sctp buffer management code")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Abel Wu <wuyun.abel@bytedance.com>
> Cc: Shakeel Butt <shakeelb@google.com>
> 
> [...]

Here is the summary with links:
  - [net] sock: annotate data-races around prot->memory_pressure
    https://git.kernel.org/netdev/net/c/76f33296d2e0

You are awesome, thank you!
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