diff mbox series

[net-next,v2] netpoll: Use rtnl_dereference() for npinfo pointer access

Message ID 20241122-netpoll_rcu_herbet_fix-v2-1-93a41fdbb19a@debian.org (mailing list archive)
State Deferred
Delegated to: Netdev Maintainers
Headers show
Series [net-next,v2] netpoll: Use rtnl_dereference() for npinfo pointer access | expand

Checks

Context Check Description
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 3 this patch: 3
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers success CCed 6 of 6 maintainers
netdev/build_clang success Errors and warnings before: 3 this patch: 3
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 5 this patch: 5
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 16 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-11-24--21-00 (tests: 790)

Commit Message

Breno Leitao Nov. 22, 2024, 1:17 p.m. UTC 
In the __netpoll_setup() function, when accessing the device's npinfo
pointer, replace rcu_access_pointer() with rtnl_dereference(). This
change is more appropriate, as suggested by Herbert Xu[1].

The function is called with the RTNL mutex held, and the pointer is
being dereferenced later, so, dereference earlier and just reuse the
pointer for the if/else.

The replacement ensures correct pointer access while maintaining
the existing locking and RCU semantics of the netpoll subsystem.

Link: https://lore.kernel.org/lkml/Zz1cKZYt1e7elibV@gondor.apana.org.au/ [1]
Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
---
Changes in v2:
- Targeting net-next instead of net
- Added the Acked-by and Reviewed-by
- Added the link in the commit summary
- Link to v1: https://lore.kernel.org/r/20241121-netpoll_rcu_herbet_fix-v1-1-457c5fee9dfd@debian.org
---
 net/core/netpoll.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)


---
base-commit: 66418447d27b7f4c027587582a133dd0bc0a663b
change-id: 20241121-netpoll_rcu_herbet_fix-3f0a433b7860

Best regards,

Comments

Eric Dumazet Nov. 22, 2024, 2:46 p.m. UTC | #1 
On Fri, Nov 22, 2024 at 2:18 PM Breno Leitao <leitao@debian.org> wrote:
>
> In the __netpoll_setup() function, when accessing the device's npinfo
> pointer, replace rcu_access_pointer() with rtnl_dereference(). This
> change is more appropriate, as suggested by Herbert Xu[1].
>
> The function is called with the RTNL mutex held, and the pointer is
> being dereferenced later, so, dereference earlier and just reuse the
> pointer for the if/else.
>
> The replacement ensures correct pointer access while maintaining
> the existing locking and RCU semantics of the netpoll subsystem.
>
> Link: https://lore.kernel.org/lkml/Zz1cKZYt1e7elibV@gondor.apana.org.au/ [1]
> Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
> Acked-by: Herbert Xu <herbert@gondor.apana.org.au>

Okay, but net-next is currently closed.
diff mbox series

Patch

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 45fb60bc4803958eb07d4038028269fc0c19622e..30152811e0903a369ccca30500e11e696be158fd 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -626,7 +626,8 @@  int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
 		goto out;
 	}
 
-	if (!rcu_access_pointer(ndev->npinfo)) {
+	npinfo = rtnl_dereference(ndev->npinfo);
+	if (!npinfo) {
 		npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);
 		if (!npinfo) {
 			err = -ENOMEM;
@@ -646,7 +647,6 @@  int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
 				goto free_npinfo;
 		}
 	} else {
-		npinfo = rtnl_dereference(ndev->npinfo);
 		refcount_inc(&npinfo->refcnt);
 	}