Re: [PATCH v3] mm/slab: Annotate kmem_cache_node->list_lock as raw

[Vlastimil Babka]

On 10/21/22 21:18, Jiri Kosina wrote:
> From: Jiri Kosina <jkosina@xxxxxxx>
> 
> The list_lock can be taken in hardirq context when do_drain() is being 
> called via IPI on all cores, and therefore lockdep complains about it, 
> because it can't be preempted on PREEMPT_RT.
> 
> That's not a real issue, as SLAB can't be built on PREEMPT_RT anyway, but 
> we still want to get rid of the warning on non-PREEMPT_RT builds.
> 
> Annotate it therefore as a raw lock in order to get rid of he lockdep 
> warning below.
> 
> 	 =============================
> 	 [ BUG: Invalid wait context ]
> 	 6.1.0-rc1-00134-ge35184f32151 #4 Not tainted
> 	 -----------------------------
> 	 swapper/3/0 is trying to lock:
> 	 ffff8bc88086dc18 (&parent->list_lock){..-.}-{3:3}, at: do_drain+0x57/0xb0
> 	 other info that might help us debug this:
> 	 context-{2:2}
> 	 no locks held by swapper/3/0.
> 	 stack backtrace:
> 	 CPU: 3 PID: 0 Comm: swapper/3 Not tainted 6.1.0-rc1-00134-ge35184f32151 #4
> 	 Hardware name: LENOVO 20K5S22R00/20K5S22R00, BIOS R0IET38W (1.16 ) 05/31/2017
> 	 Call Trace:
> 	  <IRQ>
> 	  dump_stack_lvl+0x6b/0x9d
> 	  __lock_acquire+0x1519/0x1730
> 	  ? build_sched_domains+0x4bd/0x1590
> 	  ? __lock_acquire+0xad2/0x1730
> 	  lock_acquire+0x294/0x340
> 	  ? do_drain+0x57/0xb0
> 	  ? sched_clock_tick+0x41/0x60
> 	  _raw_spin_lock+0x2c/0x40
> 	  ? do_drain+0x57/0xb0
> 	  do_drain+0x57/0xb0
> 	  __flush_smp_call_function_queue+0x138/0x220
> 	  __sysvec_call_function+0x4f/0x210
> 	  sysvec_call_function+0x4b/0x90
> 	  </IRQ>
> 	  <TASK>
> 	  asm_sysvec_call_function+0x16/0x20
> 	 RIP: 0010:mwait_idle+0x5e/0x80
> 	 Code: 31 d2 65 48 8b 04 25 80 ed 01 00 48 89 d1 0f 01 c8 48 8b 00 a8 08 75 14 66 90 0f 00 2d 0b 78 46 00 31 c0 48 89 c1 fb 0f 01 c9 <eb> 06 fb 0f 1f 44 00 00 65 48 8b 04 25 80 ed 01 00 f0 80 60 02 df
> 	 RSP: 0000:ffffa90940217ee0 EFLAGS: 00000246
> 	 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> 	 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff9bb9f93a
> 	 RBP: 0000000000000003 R08: 0000000000000001 R09: 0000000000000001
> 	 R10: ffffa90940217ea8 R11: 0000000000000000 R12: ffffffffffffffff
> 	 R13: 0000000000000000 R14: ffff8bc88127c500 R15: 0000000000000000
> 	  ? default_idle_call+0x1a/0xa0
> 	  default_idle_call+0x4b/0xa0
> 	  do_idle+0x1f1/0x2c0
> 	  ? _raw_spin_unlock_irqrestore+0x56/0x70
> 	  cpu_startup_entry+0x19/0x20
> 	  start_secondary+0x122/0x150
> 	  secondary_startup_64_no_verify+0xce/0xdb
> 	  </TASK>
> 
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>

Thanks, added to slab/for-6.2/locking

...
> diff --git a/mm/slab.h b/mm/slab.h
> index 0202a8c2f0d2..7a705e4228c8 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -750,7 +750,11 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
>   * The slab lists for all objects.
>   */
>  struct kmem_cache_node {
> +#ifdef CONFIG_SLAB
> +	raw_spinlock_t list_lock;
> +#else
>  	spinlock_t list_lock;
> +#endif
>  
>  #ifdef CONFIG_SLAB
>  	struct list_head slabs_partial;	/* partial list first, better asm code */

Simplified a bit. Since we already have CONFIG_SLAB/CONFIG_SLUB #ifdef
sections, moved the list_lock there.