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[net,0/2] netpoll: Use RCU primitives for npinfo pointer access

Message ID 20241118-netpoll_rcu-v1-0-a1888dcb4a02@debian.org (mailing list archive)
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Series netpoll: Use RCU primitives for npinfo pointer access | expand

Message

Breno Leitao Nov. 18, 2024, 11:15 a.m. UTC 
The net_device->npinfo pointer is marked with __rcu, indicating it requires
proper RCU access primitives:

  struct net_device {
	...
	struct netpoll_info __rcu *npinfo;
	...
  };

Direct access to this pointer can lead to issues such as:
- Compiler incorrectly caching/reusing stale pointer values
- Missing memory ordering guarantees
- Non-atomic pointer loads

Replace direct NULL checks of npinfo with rcu_access_pointer(),
which provides the necessary memory ordering guarantees without the
overhead of a full RCU dereference, since we only need to verify
if the pointer is NULL.

In both cases, the RCU read lock is not held when the function is being
called. I checked that by using lockdep_assert_in_rcu_read_lock(), and
seeing the warning on both cases.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Breno Leitao (2):
      netpoll: Use rcu_access_pointer() in __netpoll_setup
      netpoll: Use rcu_access_pointer() in netpoll_poll_lock

 include/linux/netpoll.h | 2 +-
 net/core/netpoll.c      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
base-commit: 8ffade77b6337a8767fae9820d57d7a6413dd1a1
change-id: 20241115-netpoll_rcu-eb1296511b71

Best regards,