Re: [PATCH bpf-next 0/3] Fix lockdep warning for htab of map

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2024-11-06 14:35:39 [+0800], Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> Hi,
Hi Hou,

> The patch set fixes a lockdep warning for htab of map. The
> warning is found when running test_maps. The warning occurs when
> htab_put_fd_value() attempts to acquire map_idr_lock to free the map id
> of the inner map while already holding the bucket lock (raw_spinlock_t).
> 
> The fix moves the invocation of free_htab_elem() after
> htab_unlock_bucket() and adds a test case to verify the solution. Please
> see the individual patches for details. Comments are always welcome.

Thank you.

Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

I've seen that you didn't move check_and_free_fields() out of the bucket
locked section. Type BPF_TIMER does hrtimer_cancel() if the timer
happens to run on a remote CPU. On PREEMPT_RT this will acquire a
sleeping lock which is problematic due to the raw_spinlock_t.
Would it be okay, to cleanup the timer unconditionally via the
workqueue?

Sebastian