linux-kernel - Re: [BUG] -next lockdep invalid wait context

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Message-ID: <ZykNhbMOrlgCXFYJ@slm.duckdns.org>
Date: Mon, 4 Nov 2024 08:08:05 -1000
From: Tejun Heo <tj@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Hillf Danton <hdanton@...a.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org
Subject: Re: [BUG] -next lockdep invalid wait context

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