From 12297f855bbd943847cb8893a3614caef5a9c2a8 Mon Sep 17 00:00:00 2001 From: Runyu Xiao Date: Tue, 27 Oct 2026 15:31:09 +0100 Subject: [PATCH] can: proc: reset pkg_stats atomics individually Commit 80b5f90158d1 ("can: statistics: use atomic access in hot path") converted several members of struct can_pkg_stats to atomic_long_t and updated the hot TX/RX and procfs read paths to use atomic_long_*() helpers. However, can_init_stats() still clears the whole struct with memset(). can_init_stats() is reached from can_stat_update() in timer context and also from the procfs reset path. Those paths can run while the TX/RX hot paths are concurrently updating rx_frames, tx_frames, matches and their *_delta counters. Hitting the whole-struct memset() in that window performs plain writes to fields that otherwise follow an atomic_long_t access contract, which can lose or mix live statistics updates. This issue was found by source-level API-misuse analysis looking for whole-object resets left behind after atomic_long_t conversions, then manually audited on Linux v6.18.21. Replace the whole-struct memset() with a helper that resets the atomic_long_t counters via atomic_long_set() and clears the derived scalar statistics explicitly. This preserves the existing reset semantics for scalar fields while restoring atomic access discipline for the live counters. Build-tested by compiling net/can/proc.o on x86_64 netdev/main. Runtime-tested with a QEMU + vcan setup on Linux v6.18.21 by driving concurrent traffic and reset_stats reads, which reproduced inconsistent exported statistics before the fix. [Hartkopp] can_stat_update() also read the *_delta counters at the beginning and cleared them with atomic_long_set() at the end. Increments from the hot path in between were lost for both the current and the next interval. Use atomic_long_xchg() to fetch and clear the *_delta counters in one atomic step instead. On x86_64 atomic_long_set() is a plain store like memset(), so the memset() is an actual problem only on architectures with lock-based atomics (e.g. parisc). The inconsistencies seen on x86_64 come from the *_delta handling and from the stale snapshots, which are fixed in "can: proc: skip stats calculation after reset in can_stat_update()". As before, the counters are reset one at a time and the derived scalar statistics use plain stores. Fixes: 80b5f90158d1 ("can: statistics: use atomic access in hot path") Cc: stable@vger.kernel.org Signed-off-by: Runyu Xiao Acked-by: Oliver Hartkopp Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20261027-can-rx-lock-v12-5-eb5afc2d8b9b@hartkopp.net Signed-off-by: Marc Kleine-Budde --- net/can/proc.c | 39 +++++++++++++++++++++++++++++---------- 1 file changed, 29 insertions(+), 10 deletions(-) diff --git a/net/can/proc.c b/net/can/proc.c index de4d05ae3459..70104f13077e 100644 --- a/net/can/proc.c +++ b/net/can/proc.c @@ -76,16 +76,39 @@ static const char rx_list_name[][8] = { * af_can statistics stuff */ +static void can_reset_pkg_stats(struct can_pkg_stats *pkg_stats) +{ + atomic_long_set(&pkg_stats->rx_frames, 0); + atomic_long_set(&pkg_stats->tx_frames, 0); + atomic_long_set(&pkg_stats->matches, 0); + + pkg_stats->total_rx_rate = 0; + pkg_stats->total_tx_rate = 0; + pkg_stats->total_rx_match_ratio = 0; + + pkg_stats->current_rx_rate = 0; + pkg_stats->current_tx_rate = 0; + pkg_stats->current_rx_match_ratio = 0; + + pkg_stats->max_rx_rate = 0; + pkg_stats->max_tx_rate = 0; + pkg_stats->max_rx_match_ratio = 0; + + atomic_long_set(&pkg_stats->rx_frames_delta, 0); + atomic_long_set(&pkg_stats->tx_frames_delta, 0); + atomic_long_set(&pkg_stats->matches_delta, 0); +} + static void can_init_stats(struct net *net) { struct can_pkg_stats *pkg_stats = net->can.pkg_stats; struct can_rcv_lists_stats *rcv_lists_stats = net->can.rcv_lists_stats; /* - * This memset function is called from a timer context (when + * This stats reset is called from a timer context (when * can_stattimer is active which is the default) OR in a process * context (reading the proc_fs when can_stattimer is disabled). */ - memset(pkg_stats, 0, sizeof(struct can_pkg_stats)); + can_reset_pkg_stats(pkg_stats); pkg_stats->jiffies_init = jiffies; rcv_lists_stats->stats_reset++; @@ -121,9 +144,10 @@ void can_stat_update(struct timer_list *t) long rx_frames = atomic_long_read(&pkg_stats->rx_frames); long tx_frames = atomic_long_read(&pkg_stats->tx_frames); long matches = atomic_long_read(&pkg_stats->matches); - long rx_frames_delta = atomic_long_read(&pkg_stats->rx_frames_delta); - long tx_frames_delta = atomic_long_read(&pkg_stats->tx_frames_delta); - long matches_delta = atomic_long_read(&pkg_stats->matches_delta); + /* fetch and clear values for 'current rate' calculation */ + long rx_frames_delta = atomic_long_xchg(&pkg_stats->rx_frames_delta, 0); + long tx_frames_delta = atomic_long_xchg(&pkg_stats->tx_frames_delta, 0); + long matches_delta = atomic_long_xchg(&pkg_stats->matches_delta, 0); /* restart counting in timer context on user request */ if (user_reset) @@ -172,11 +196,6 @@ void can_stat_update(struct timer_list *t) if (pkg_stats->max_rx_match_ratio < pkg_stats->current_rx_match_ratio) pkg_stats->max_rx_match_ratio = pkg_stats->current_rx_match_ratio; - /* clear values for 'current rate' calculation */ - atomic_long_set(&pkg_stats->tx_frames_delta, 0); - atomic_long_set(&pkg_stats->rx_frames_delta, 0); - atomic_long_set(&pkg_stats->matches_delta, 0); - /* restart timer (one second) */ mod_timer(&net->can.stattimer, round_jiffies(jiffies + HZ)); }