From: Eric Dumazet Date: Wed, 27 Aug 2025 16:23:52 +0000 (+0000) Subject: net_sched: gen_estimator: fix est_timer() vs CONFIG_PREEMPT_RT=y X-Git-Tag: v6.17-rc5~21^2~46 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=9f74c0ea9b26d1505d55b61e36b1623dd347e1d1;p=users%2Fgriffoul%2Flinux.git net_sched: gen_estimator: fix est_timer() vs CONFIG_PREEMPT_RT=y syzbot reported a WARNING in est_timer() [1] Problem here is that with CONFIG_PREEMPT_RT=y, timer callbacks can be preempted. Adopt preempt_disable_nested()/preempt_enable_nested() to fix this. [1] WARNING: CPU: 0 PID: 16 at ./include/linux/seqlock.h:221 __seqprop_assert include/linux/seqlock.h:221 [inline] WARNING: CPU: 0 PID: 16 at ./include/linux/seqlock.h:221 est_timer+0x6dc/0x9f0 net/core/gen_estimator.c:93 Modules linked in: CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:__seqprop_assert include/linux/seqlock.h:221 [inline] RIP: 0010:est_timer+0x6dc/0x9f0 net/core/gen_estimator.c:93 Call Trace: call_timer_fn+0x17e/0x5f0 kernel/time/timer.c:1747 expire_timers kernel/time/timer.c:1798 [inline] __run_timers kernel/time/timer.c:2372 [inline] __run_timer_base+0x648/0x970 kernel/time/timer.c:2384 run_timer_base kernel/time/timer.c:2393 [inline] run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403 handle_softirqs+0x22c/0x710 kernel/softirq.c:579 __do_softirq kernel/softirq.c:613 [inline] run_ktimerd+0xcf/0x190 kernel/softirq.c:1043 smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:160 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.") Reported-by: syzbot+72db9ee39db57c3fecc5@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68adf6fa.a70a0220.3cafd4.0000.GAE@google.com/T/#u Signed-off-by: Eric Dumazet Reviewed-by: Sebastian Andrzej Siewior Link: https://patch.msgid.link/20250827162352.3960779-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c index 7d426a8e29f3..f112156db587 100644 --- a/net/core/gen_estimator.c +++ b/net/core/gen_estimator.c @@ -90,10 +90,12 @@ static void est_timer(struct timer_list *t) rate = (b_packets - est->last_packets) << (10 - est->intvl_log); rate = (rate >> est->ewma_log) - (est->avpps >> est->ewma_log); + preempt_disable_nested(); write_seqcount_begin(&est->seq); est->avbps += brate; est->avpps += rate; write_seqcount_end(&est->seq); + preempt_enable_nested(); est->last_bytes = b_bytes; est->last_packets = b_packets;