On Sun, 28 Dec 2025 14:50:07 +0800
Wupeng Ma <[email protected]> wrote:
> When user resize all trace ring buffer through file 'buffer_size_kb',
> then in ring_buffer_resize(), kernel allocates buffer pages for each
> cpu in a loop.
>
> If the kernel preemption model is PREEMPT_NONE and there are many cpus
> and there are many buffer pages to be freed, it may not give up cpu
> for a long time and finally cause a softlockup.
>
> To avoid it, call cond_resched() after each cpu buffer free as Commit
> f6bd2c92488c ("ring-buffer: Avoid softlockup in ring_buffer_resize()")
> does.
>
> Detailed call trace as follow:
>
> rcu: INFO: rcu_sched self-detected stall on CPU
> rcu: 24-....: (14837 ticks this GP) idle=521c/1/0x4000000000000000
> softirq=230597/230597 fqs=5329
> rcu: (t=15004 jiffies g=26003221 q=211022 ncpus=96)
> CPU: 24 UID: 0 PID: 11253 Comm: bash Kdump: loaded Tainted: G EL
> 6.18.2+ #278 NONE
> pc : arch_local_irq_restore+0x8/0x20
> arch_local_irq_restore+0x8/0x20 (P)
> free_frozen_page_commit+0x28c/0x3b0
> __free_frozen_pages+0x1c0/0x678
> ___free_pages+0xc0/0xe0
> free_pages+0x3c/0x50
> ring_buffer_resize.part.0+0x6a8/0x880
> ring_buffer_resize+0x3c/0x58
> __tracing_resize_ring_buffer.part.0+0x34/0xd8
> tracing_resize_ring_buffer+0x8c/0xd0
> tracing_entries_write+0x74/0xd8
> vfs_write+0xcc/0x288
> ksys_write+0x74/0x118
> __arm64_sys_write+0x24/0x38
>
> Signed-off-by: Wupeng Ma <[email protected]>
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Thanks!
> ---
> kernel/trace/ring_buffer.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index afcd3747264d2..3ba08fc1b7d05 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -3121,6 +3121,8 @@ int ring_buffer_resize(struct trace_buffer *buffer,
> unsigned long size,
> list) {
> list_del_init(&bpage->list);
> free_buffer_page(bpage);
> +
> + cond_resched();
> }
> }
> out_err_unlock:
> --
> 2.43.0
>
--
Masami Hiramatsu (Google) <[email protected]>
