* [PATCH] lib/sys_info: avoid showing locks info twice in __sys_info
@ 2026-11-13 15:14 Leon Hwang
2026-11-13 16:40 ` Lance Yang
0 siblings, 1 reply; 2+ messages in thread
From: Leon Hwang @ 2026-11-13 15:14 UTC (permalink / raw)
To: Andrew Morton, Feng Tang; +Cc: Lance Yang, linux-kernel, Leon Hwang
In __sys_info(), if the si_mask has both SYS_INFO_TASKS and SYS_INFO_LOCKS,
the locks info will be printed twice: debug_show_all_locks() is also
called inner show_state().
Since commit
8b2b9b4f6f4f ("hung_task: add hung_task_sys_info sysctl to dump sys info on task-hung"),
hung_task will print locks info twice when
sysctl -w kernel.hung_task_sys_info="tasks,locks".
[ 4658.894440]
Showing all locks held in the system:
[ 4658.894445] locks held by khungtaskd/119: 1, last CPU#7:
[ 4658.894449] #0: ffffffff9159cd00 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3b/0x1f0
[ 4658.894468] locks held by cat/674: 1, on CPU#8:
[ 4658.894472] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
[ 4658.894487] locks held by cat/676: 1, on CPU#8:
[ 4658.894490] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
[ 4658.894504] locks held by dmesg/677: 5, last CPU#8:
[ 4658.894507] #0: ff426e3f828ee0a0 (&tty->ldisc_sem){++++}-{0:0}, at: ldsem_down_read+0x34/0x40
[ 4658.894521] #1: ff426e3f828ee128 (&tty->atomic_write_lock){+.+.}-{4:4}, at: file_tty_write.isra.0+0xaa/0x360
[ 4658.894535] #2: ff426e3f828ee2c8 (&tty->termios_rwsem){++++}-{4:4}, at: n_tty_write+0x9d/0x4c0
[ 4658.894549] #3: ff4fe07e82c57370 (&ldata->output_lock){+.+.}-{4:4}, at: remove_wait_queue+0x1b/0x60
[ 4658.894563] #4: ffffffff927b1278 (&port_lock_key){-.-.}-{3:3}, at: uart_write_room+0x4e/0x230
[ 4658.894581] =============================================
[ 4658.894583]
Showing all locks held in the system:
[ 4658.894586] locks held by khungtaskd/119: 1, last CPU#7:
[ 4658.894589] #0: ffffffff9159cd00 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3b/0x1f0
[ 4658.894604] locks held by cat/674: 1, on CPU#8:
[ 4658.894607] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
[ 4658.894622] locks held by cat/676: 1, on CPU#8:
[ 4658.894625] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
[ 4658.894639] locks held by dmesg/677: 5, last CPU#8:
[ 4658.894642] #0: ff426e3f828ee0a0 (&tty->ldisc_sem){++++}-{0:0}, at: ldsem_down_read+0x34/0x40
[ 4658.894655] #1: ff426e3f828ee128 (&tty->atomic_write_lock){+.+.}-{4:4}, at: file_tty_write.isra.0+0xaa/0x360
[ 4658.894669] #2: ff426e3f828ee2c8 (&tty->termios_rwsem){++++}-{4:4}, at: n_tty_write+0x9d/0x4c0
[ 4658.894683] #3: ff4fe07e82c57370 (&ldata->output_lock){+.+.}-{4:4}, at: n_tty_write+0x190/0x4c0
[ 4658.894697] #4: ffffffff927b1278 (&port_lock_key){-.-.}-{3:3}, at: uart_write_room+0x4e/0x230
[ 4658.894713] =============================================
To avoid showing locks info again, check '!(si_mask & SYS_INFO_TASKS)'
when checking 'si_mask & SYS_INFO_LOCKS' in __sys_info().
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
lib/sys_info.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/sys_info.c b/lib/sys_info.c
index f32a06ec9ed4..750803012f43 100644
--- a/lib/sys_info.c
+++ b/lib/sys_info.c
@@ -147,7 +147,7 @@ static void __sys_info(unsigned long si_mask)
if (si_mask & SYS_INFO_TIMERS)
sysrq_timer_list_show();
- if (si_mask & SYS_INFO_LOCKS)
+ if ((si_mask & SYS_INFO_LOCKS) && !(si_mask & SYS_INFO_TASKS))
debug_show_all_locks();
if (si_mask & SYS_INFO_FTRACE)
--
2.55.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] lib/sys_info: avoid showing locks info twice in __sys_info
2026-11-13 15:14 [PATCH] lib/sys_info: avoid showing locks info twice in __sys_info Leon Hwang
@ 2026-11-13 16:40 ` Lance Yang
0 siblings, 0 replies; 2+ messages in thread
From: Lance Yang @ 2026-11-13 16:40 UTC (permalink / raw)
To: leon.hwang; +Cc: akpm, feng.tang, lance.yang, linux-kernel
On Fri, Nov 13, 2026 at 11:14:51PM +0800, Leon Hwang wrote:
>In __sys_info(), if the si_mask has both SYS_INFO_TASKS and SYS_INFO_LOCKS,
>the locks info will be printed twice: debug_show_all_locks() is also
>called inner show_state().
Good catch!
>Since commit
>8b2b9b4f6f4f ("hung_task: add hung_task_sys_info sysctl to dump sys info on task-hung"),
>hung_task will print locks info twice when
>sysctl -w kernel.hung_task_sys_info="tasks,locks".
>
>[ 4658.894440]
> Showing all locks held in the system:
>[ 4658.894445] locks held by khungtaskd/119: 1, last CPU#7:
>[ 4658.894449] #0: ffffffff9159cd00 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3b/0x1f0
>[ 4658.894468] locks held by cat/674: 1, on CPU#8:
>[ 4658.894472] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
>[ 4658.894487] locks held by cat/676: 1, on CPU#8:
>[ 4658.894490] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
>[ 4658.894504] locks held by dmesg/677: 5, last CPU#8:
>[ 4658.894507] #0: ff426e3f828ee0a0 (&tty->ldisc_sem){++++}-{0:0}, at: ldsem_down_read+0x34/0x40
>[ 4658.894521] #1: ff426e3f828ee128 (&tty->atomic_write_lock){+.+.}-{4:4}, at: file_tty_write.isra.0+0xaa/0x360
>[ 4658.894535] #2: ff426e3f828ee2c8 (&tty->termios_rwsem){++++}-{4:4}, at: n_tty_write+0x9d/0x4c0
>[ 4658.894549] #3: ff4fe07e82c57370 (&ldata->output_lock){+.+.}-{4:4}, at: remove_wait_queue+0x1b/0x60
>[ 4658.894563] #4: ffffffff927b1278 (&port_lock_key){-.-.}-{3:3}, at: uart_write_room+0x4e/0x230
>
>[ 4658.894581] =============================================
>
>[ 4658.894583]
> Showing all locks held in the system:
>[ 4658.894586] locks held by khungtaskd/119: 1, last CPU#7:
>[ 4658.894589] #0: ffffffff9159cd00 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3b/0x1f0
>[ 4658.894604] locks held by cat/674: 1, on CPU#8:
>[ 4658.894607] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
>[ 4658.894622] locks held by cat/676: 1, on CPU#8:
>[ 4658.894625] #0: ffffffffc01681a0 (dummy_mutex){+.+.}-{4:4}, at: read_dummy_mutex+0x34/0x80 [hung_task_tests]
>[ 4658.894639] locks held by dmesg/677: 5, last CPU#8:
>[ 4658.894642] #0: ff426e3f828ee0a0 (&tty->ldisc_sem){++++}-{0:0}, at: ldsem_down_read+0x34/0x40
>[ 4658.894655] #1: ff426e3f828ee128 (&tty->atomic_write_lock){+.+.}-{4:4}, at: file_tty_write.isra.0+0xaa/0x360
>[ 4658.894669] #2: ff426e3f828ee2c8 (&tty->termios_rwsem){++++}-{4:4}, at: n_tty_write+0x9d/0x4c0
>[ 4658.894683] #3: ff4fe07e82c57370 (&ldata->output_lock){+.+.}-{4:4}, at: n_tty_write+0x190/0x4c0
>[ 4658.894697] #4: ffffffff927b1278 (&port_lock_key){-.-.}-{3:3}, at: uart_write_room+0x4e/0x230
>
>[ 4658.894713] =============================================
>
>To avoid showing locks info again, check '!(si_mask & SYS_INFO_TASKS)'
>when checking 'si_mask & SYS_INFO_LOCKS' in __sys_info().
>
>Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
>---
> lib/sys_info.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/lib/sys_info.c b/lib/sys_info.c
>index f32a06ec9ed4..750803012f43 100644
>--- a/lib/sys_info.c
>+++ b/lib/sys_info.c
>@@ -147,7 +147,7 @@ static void __sys_info(unsigned long si_mask)
> if (si_mask & SYS_INFO_TIMERS)
> sysrq_timer_list_show();
>
>- if (si_mask & SYS_INFO_LOCKS)
>+ if ((si_mask & SYS_INFO_LOCKS) && !(si_mask & SYS_INFO_TASKS))
> debug_show_all_locks();
LGTM, thanks!
Reviewed-by: Lance Yang <lance.yang@linux.dev>
>
> if (si_mask & SYS_INFO_FTRACE)
>--
>2.55.0
>
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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