From: Eric Dumazet Date: Wed, 22 Jul 2026 14:17:43 +0000 (+0000) Subject: drop_monitor: perform u64_stats updates under IRQ-disabled section X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=fd098a23bf8fda7eae48db9b06e7c34fc4d228fa;p=thirdparty%2Flinux.git drop_monitor: perform u64_stats updates under IRQ-disabled section In net_dm_packet_trace_kfree_skb_hit() and net_dm_hw_trap_packet_probe(), u64_stats_update_begin() / u64_stats_inc() / u64_stats_update_end() were called after spin_unlock_irqrestore(&...drop_queue.lock, flags), when local IRQs had already been re-enabled. Tracepoint probes can execute in IRQ or softirq context. On 32-bit architectures, u64_stats_update_begin() disables preemption but not interrupts, relying on seqcount writes. If a nested interrupt occurs on the same CPU during the 64-bit stats update, the reentrant seqcount update can corrupt the seqcount state or stats value. Fix this by performing the 64-bit per-CPU stats update before releasing drop_queue.lock via spin_unlock_irqrestore(), ensuring local interrupts remain disabled during the u64_stats update. Fixes: e9feb58020f9 ("drop_monitor: Expose tail drop counter") Fixes: 5e58109b1ea4 ("drop_monitor: Add support for packet alert mode for hardware drops") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260722141743.3266924-3-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c index 9abcdee8c76e..abaf108ac4db 100644 --- a/net/core/drop_monitor.c +++ b/net/core/drop_monitor.c @@ -530,10 +530,10 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore, return; unlock_free: - spin_unlock_irqrestore(&data->drop_queue.lock, flags); u64_stats_update_begin(&data->stats.syncp); u64_stats_inc(&data->stats.dropped); u64_stats_update_end(&data->stats.syncp); + spin_unlock_irqrestore(&data->drop_queue.lock, flags); consume_skb(nskb); } @@ -997,10 +997,10 @@ net_dm_hw_trap_packet_probe(void *ignore, const struct devlink *devlink, return; unlock_free: - spin_unlock_irqrestore(&hw_data->drop_queue.lock, flags); u64_stats_update_begin(&hw_data->stats.syncp); u64_stats_inc(&hw_data->stats.dropped); u64_stats_update_end(&hw_data->stats.syncp); + spin_unlock_irqrestore(&hw_data->drop_queue.lock, flags); net_dm_hw_metadata_free(n_hw_metadata); free: consume_skb(nskb);