Date: Mon, 8 Apr 2024 16:41:24 +0100
From: Simon Horman <horms@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, eric.dumazet@...il.com,
	Marek Lindner <mareklindner@...mailbox.ch>,
	Simon Wunderlich <sw@...onwunderlich.de>,
	Antonio Quartulli <a@...table.cc>,
	Sven Eckelmann <sven@...fation.org>
Subject: Re: [PATCH net-next] batman-adv: bypass empty buckets in
 batadv_purge_orig_ref()

On Sat, Mar 30, 2024 at 03:54:38PM +0000, Eric Dumazet wrote:
> Many syzbot reports are pointing to soft lockups in
> batadv_purge_orig_ref() [1]
> 
> Root cause is unknown, but we can avoid spending too much
> time there and perhaps get more interesting reports.
> 
> [1]
> 
> watchdog: BUG: soft lockup - CPU#0 stuck for 27s! [kworker/u4:6:621]
> Modules linked in:
> irq event stamp: 6182794
>  hardirqs last  enabled at (6182793): [<ffff8000801dae10>] __local_bh_enable_ip+0x224/0x44c kernel/softirq.c:386
>  hardirqs last disabled at (6182794): [<ffff80008ad66a78>] __el1_irq arch/arm64/kernel/entry-common.c:533 [inline]
>  hardirqs last disabled at (6182794): [<ffff80008ad66a78>] el1_interrupt+0x24/0x68 arch/arm64/kernel/entry-common.c:551
>  softirqs last  enabled at (6182792): [<ffff80008aab71c4>] spin_unlock_bh include/linux/spinlock.h:396 [inline]
>  softirqs last  enabled at (6182792): [<ffff80008aab71c4>] batadv_purge_orig_ref+0x114c/0x1228 net/batman-adv/originator.c:1287
>  softirqs last disabled at (6182790): [<ffff80008aab61dc>] spin_lock_bh include/linux/spinlock.h:356 [inline]
>  softirqs last disabled at (6182790): [<ffff80008aab61dc>] batadv_purge_orig_ref+0x164/0x1228 net/batman-adv/originator.c:1271
> CPU: 0 PID: 621 Comm: kworker/u4:6 Not tainted 6.8.0-rc7-syzkaller-g707081b61156 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
> Workqueue: bat_events batadv_purge_orig
> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>  pc : should_resched arch/arm64/include/asm/preempt.h:79 [inline]
>  pc : __local_bh_enable_ip+0x228/0x44c kernel/softirq.c:388
>  lr : __local_bh_enable_ip+0x224/0x44c kernel/softirq.c:386
> sp : ffff800099007970
> x29: ffff800099007980 x28: 1fffe00018fce1bd x27: dfff800000000000
> x26: ffff0000d2620008 x25: ffff0000c7e70de8 x24: 0000000000000001
> x23: 1fffe00018e57781 x22: dfff800000000000 x21: ffff80008aab71c4
> x20: ffff0001b40136c0 x19: ffff0000c72bbc08 x18: 1fffe0001a817bb0
> x17: ffff800125414000 x16: ffff80008032116c x15: 0000000000000001
> x14: 1fffe0001ee9d610 x13: 0000000000000000 x12: 0000000000000003
> x11: 0000000000000000 x10: 0000000000ff0100 x9 : 0000000000000000
> x8 : 00000000005e5789 x7 : ffff80008aab61dc x6 : 0000000000000000
> x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
> x2 : 0000000000000006 x1 : 0000000000000080 x0 : ffff800125414000
> Call trace:
>   __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:27 [inline]
>   arch_local_irq_enable arch/arm64/include/asm/irqflags.h:49 [inline]
>   __local_bh_enable_ip+0x228/0x44c kernel/softirq.c:386
>   __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
>   _raw_spin_unlock_bh+0x3c/0x4c kernel/locking/spinlock.c:210
>   spin_unlock_bh include/linux/spinlock.h:396 [inline]
>   batadv_purge_orig_ref+0x114c/0x1228 net/batman-adv/originator.c:1287
>   batadv_purge_orig+0x20/0x70 net/batman-adv/originator.c:1300
>   process_one_work+0x694/0x1204 kernel/workqueue.c:2633
>   process_scheduled_works kernel/workqueue.c:2706 [inline]
>   worker_thread+0x938/0xef4 kernel/workqueue.c:2787
>   kthread+0x288/0x310 kernel/kthread.c:388
>   ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.8.0-rc7-syzkaller-g707081b61156 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>  pc : arch_local_irq_enable+0x8/0xc arch/arm64/include/asm/irqflags.h:51
>  lr : default_idle_call+0xf8/0x128 kernel/sched/idle.c:103
> sp : ffff800093a17d30
> x29: ffff800093a17d30 x28: dfff800000000000 x27: 1ffff00012742fb4
> x26: ffff80008ec9d000 x25: 0000000000000000 x24: 0000000000000002
> x23: 1ffff00011d93a74 x22: ffff80008ec9d3a0 x21: 0000000000000000
> x20: ffff0000c19dbc00 x19: ffff8000802d0fd8 x18: 1fffe00036804396
> x17: ffff80008ec9d000 x16: ffff8000802d089c x15: 0000000000000001
> x14: 1fffe00036805f10 x13: 0000000000000000 x12: 0000000000000003
> x11: 0000000000000001 x10: 0000000000000003 x9 : 0000000000000000
> x8 : 00000000000ce8d1 x7 : ffff8000804609e4 x6 : 0000000000000000
> x5 : 0000000000000001 x4 : 0000000000000001 x3 : ffff80008ad6aac0
> x2 : 0000000000000000 x1 : ffff80008aedea60 x0 : ffff800125436000
> Call trace:
>   __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:27 [inline]
>   arch_local_irq_enable+0x8/0xc arch/arm64/include/asm/irqflags.h:49
>   cpuidle_idle_call kernel/sched/idle.c:170 [inline]
>   do_idle+0x1f0/0x4e8 kernel/sched/idle.c:312
>   cpu_startup_entry+0x5c/0x74 kernel/sched/idle.c:410
>   secondary_start_kernel+0x198/0x1c0 arch/arm64/kernel/smp.c:272
>   __secondary_switched+0xb8/0xbc arch/arm64/kernel/head.S:404
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Marek Lindner <mareklindner@...mailbox.ch>
> Cc: Simon Wunderlich <sw@...onwunderlich.de>
> Cc: Antonio Quartulli <a@...table.cc>
> Cc: Sven Eckelmann <sven@...fation.org>

Reviewed-by: Simon Horman <horms@...nel.org>

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