Re: [BUG] -next lockdep invalid wait context

[Tejun Heo <tj@kernel.org>]

Hello,

On Fri, Nov 01, 2024 at 05:45:01PM -0700, Boqun Feng wrote:
...
> Because it's a different bug.
> 
> 	schedule():
> 	  __schedule():
> 	    rq_lock(); // <- rq lock is a raw spin lock, so no sleep inside
> 	    switch_mm_irqs_off():
> 	      trace_tlb_flush():
> 	        bpf_trace_run2():
> 		  stack_map_get_build_id_offset():
> 		    mmap_read_trylock(): // this is actually ok, because
> 		    			 // trylock() on rwsem won't
> 					 // sleep.
> 		      __mmap_lock_trace_acquire_returned():
> 		        get_mm_memcg_path():
> 			  cgroup_path():
> 			    kernfs_path_from_node():
> 			      read_lock_irqsave(); // on RT, read_lock()
> 			      			   // is a rwsem IIUC,
> 						   // so might sleep.
> 						   // hence the issue.
> 
> Maybe kernfs can use RCU instead of read_lock here? I don't know...

Yeah, we should be able to make kn->name RCU protected and drop the usage of
the rename lock in read paths.

Thanks.

-- 
tejun