diff mbox series

[net-next,6/8] rtnetlink: do not depend on RTNL in rtnl_fill_proto_down()

Message ID 20240503192059.3884225-7-edumazet@google.com (mailing list archive)
State Accepted
Commit 6890ab31d1a35444741e6150db19d64797db2919
Delegated to: Netdev Maintainers
Headers show
Series rtnetlink: more rcu conversions for rtnl_fill_ifinfo() | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
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: 933 this patch: 933
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers success CCed 4 of 4 maintainers
netdev/build_clang success Errors and warnings before: 938 this patch: 938
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: 944 this patch: 944
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 54 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 85 this patch: 85
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-05-05--03-00 (tests: 1003)

Commit Message

Eric Dumazet May 3, 2024, 7:20 p.m. UTC 
Change dev_change_proto_down() and dev_change_proto_down_reason()
to write once on dev->proto_down and dev->proto_down_reason.

Then rtnl_fill_proto_down() can use READ_ONCE() annotations
and run locklessly.

rtnl_proto_down_size() should assume worst case,
because readng dev->proto_down_reason multiple
times would be racy without RTNL in the future.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/dev.c       | 11 +++++++----
 net/core/rtnetlink.c |  8 ++++----
 2 files changed, 11 insertions(+), 8 deletions(-)

Comments

Simon Horman May 5, 2024, 2:52 p.m. UTC | #1 
On Fri, May 03, 2024 at 07:20:57PM +0000, Eric Dumazet wrote:
> Change dev_change_proto_down() and dev_change_proto_down_reason()
> to write once on dev->proto_down and dev->proto_down_reason.
> 
> Then rtnl_fill_proto_down() can use READ_ONCE() annotations
> and run locklessly.
> 
> rtnl_proto_down_size() should assume worst case,
> because readng dev->proto_down_reason multiple
> times would be racy without RTNL in the future.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Simon Horman <horms@kernel.org>
diff mbox series

Patch

diff --git a/net/core/dev.c b/net/core/dev.c
index 35ce603ffc57fa209dc9a57e60981a2bca5e6a29..06304f07146c7f672573a977b069e7f2c031122e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9223,7 +9223,7 @@  int dev_change_proto_down(struct net_device *dev, bool proto_down)
 		netif_carrier_off(dev);
 	else
 		netif_carrier_on(dev);
-	dev->proto_down = proto_down;
+	WRITE_ONCE(dev->proto_down, proto_down);
 	return 0;
 }
 
@@ -9237,18 +9237,21 @@  int dev_change_proto_down(struct net_device *dev, bool proto_down)
 void dev_change_proto_down_reason(struct net_device *dev, unsigned long mask,
 				  u32 value)
 {
+	u32 proto_down_reason;
 	int b;
 
 	if (!mask) {
-		dev->proto_down_reason = value;
+		proto_down_reason = value;
 	} else {
+		proto_down_reason = dev->proto_down_reason;
 		for_each_set_bit(b, &mask, 32) {
 			if (value & (1 << b))
-				dev->proto_down_reason |= BIT(b);
+				proto_down_reason |= BIT(b);
 			else
-				dev->proto_down_reason &= ~BIT(b);
+				proto_down_reason &= ~BIT(b);
 		}
 	}
+	WRITE_ONCE(dev->proto_down_reason, proto_down_reason);
 }
 
 struct bpf_xdp_link {
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 242c24e857ec4c799f0239be3371fd589a8ed191..6af7f00503b43d4989d0aaafc8b968216a6e77f5 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1036,8 +1036,8 @@  static size_t rtnl_proto_down_size(const struct net_device *dev)
 {
 	size_t size = nla_total_size(1);
 
-	if (dev->proto_down_reason)
-		size += nla_total_size(0) + nla_total_size(4);
+	/* Assume dev->proto_down_reason is not zero. */
+	size += nla_total_size(0) + nla_total_size(4);
 
 	return size;
 }
@@ -1737,10 +1737,10 @@  static int rtnl_fill_proto_down(struct sk_buff *skb,
 	struct nlattr *pr;
 	u32 preason;
 
-	if (nla_put_u8(skb, IFLA_PROTO_DOWN, dev->proto_down))
+	if (nla_put_u8(skb, IFLA_PROTO_DOWN, READ_ONCE(dev->proto_down)))
 		goto nla_put_failure;
 
-	preason = dev->proto_down_reason;
+	preason = READ_ONCE(dev->proto_down_reason);
 	if (!preason)
 		return 0;