Re: [PATCH -v2] lockdep: Enable the printing of held locks of remote running tasks and print task CPU

[Ingo Molnar]

* Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:

> On 2026/07/07 16:20, Ingo Molnar wrote:
> > TL;DR: it should be fine to print the held locks of running
> > tasks too, as long as we print out a warning when we print
> > such a task, so that users are aware of any racy output.
> 
> Is there a warning we print out?
> We dropped WARNING: in this version, didn't we?

Indeed - I fixed the changelog.

> > Finally, print out the last CPU a task has ran on. This is very
> > useful information for races and for locking bugs in particular.
> > This basically extends the 'on CPU#%d' message we print for
> > running tasks to all tasks we print.
> 
> I like this change. Thank you. ;-)
> 
> # echo t > /proc/sysrq-trigger; sleep 3; dmesg -c | cut -b 15-
> 
> Before:
> 
>  Showing all locks held in the system:
>  4 locks held by pr/legacy/16:
>  1 lock held by rcub/1/18:
>   #0: ffffffff92ba36c8 (rcu_state){+.+.}-{0:0}, at: rcu_boost_kthread+0x15c/0x5d0
>  3 locks held by bash/1221:
>   #0: ffff8cd5dd8df500 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x9a/0x150
>   #1: ffffffff92b9e080 (rcu_read_lock){....}-{1:3}, at: __handle_sysrq+0x56/0x140
>   #2: ffffffff92b9e080 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184
> 
> After:
> 
>  Showing all locks held in the system:
>  locks held by pr/legacy/16: 4, last CPU#0:
>   #0: ffffffffaaf9a4a0 (console_lock){+.+.}-{0:0}, at: legacy_kthread_func+0x85/0x190
>   #1: ffffffffaaf9a4f8 (console_srcu){....}-{0:0}, at: console_flush_one_record+0x92/0x710
>   #2: ffffffffab1fb818 (printing_lock){+.+.}-{3:3}, at: vt_console_print+0x74/0x640
>   #3: ffffffffaaf9e080 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x61/0x140
>  locks held by rcub/1/18: 1, on CPU#0:
>   #0: ffffffffaafa36c8 (rcu_state){+.+.}-{0:0}, at: rcu_boost_kthread+0x15c/0x5d0
>  locks held by bash/1206: 3, last CPU#0:
>   #0: ffff8c62894da500 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x9a/0x150
>   #1: ffffffffaaf9e080 (rcu_read_lock){....}-{1:3}, at: __handle_sysrq+0x56/0x140
>   #2: ffffffffaaf9e080 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184

Great, and you are welcome.

I've added your Tested-by tag as well, and graduated the updated
commit to tip:locking/core, to be merged into v7.3 if everything
goes fine.

Thanks,

	Ingo