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 <mawupeng1@huawei.com>
---
 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

On Sun, 28 Dec 2025 14:50:07 +0800
Wupeng Ma <mawupeng1@huawei.com> 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 <mawupeng1@huawei.com>

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

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) <mhiramat@kernel.org>