Re: [PATCH] mm: fix sleeping function warning in alloc_swap_info

[Aaron Lu <aaron.lu@linux.alibaba.com>]

On 2019/1/29 15:21, Jiufei Xue wrote:
> Trinity reports BUG:
> 
> sleeping function called from invalid context at mm/vmalloc.c:1477
> in_atomic(): 1, irqs_disabled(): 0, pid: 12269, name: trinity-c1
> 
> [ 2748.573460] Call Trace:
> [ 2748.575935]  dump_stack+0x91/0xeb
> [ 2748.578512]  ___might_sleep+0x21c/0x250
> [ 2748.581090]  remove_vm_area+0x1d/0x90
> [ 2748.583637]  __vunmap+0x76/0x100
> [ 2748.586120]  __se_sys_swapon+0xb9a/0x1220
> [ 2748.598973]  do_syscall_64+0x60/0x210
> [ 2748.601439]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> This is triggered by calling kvfree() inside spinlock() section in
> function alloc_swap_info().
> Fix this by moving the kvfree() after spin_unlock().

The fix looks good to me.

BTW, swap_info_struct's size has been reduced to its original size:
272 bytes by commit 66f71da9dd38("mm/swap: use nr_node_ids for
avail_lists in swap_info_struct"). I didn't use back kzalloc/kfree
in that commit since I don't see any any harm by keep using
kvzalloc/kvfree, but now looks like they're causing some trouble.

So what about using back kzalloc/kfree for swap_info_struct instead?
Can save one local variable and using kvzalloc/kvfree for a struct
that is 272 bytes doesn't really have any benefit.

Thanks,
Aaron

> 
> Fixes: 873d7bcfd066 ("mm/swapfile.c: use kvzalloc for swap_info_struct allocation")
> Cc: <stable@vger.kernel.org>
> Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
> ---
>  mm/swapfile.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index dbac1d49469d..d26c9eac3d64 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2810,7 +2810,7 @@ late_initcall(max_swapfiles_check);
>  
>  static struct swap_info_struct *alloc_swap_info(void)
>  {
> -	struct swap_info_struct *p;
> +	struct swap_info_struct *p, *tmp = NULL;
>  	unsigned int type;
>  	int i;
>  	int size = sizeof(*p) + nr_node_ids * sizeof(struct plist_node);
> @@ -2840,7 +2840,7 @@ static struct swap_info_struct *alloc_swap_info(void)
>  		smp_wmb();
>  		nr_swapfiles++;
>  	} else {
> -		kvfree(p);
> +		tmp = p;
>  		p = swap_info[type];
>  		/*
>  		 * Do not memset this entry: a racing procfs swap_next()
> @@ -2853,6 +2853,8 @@ static struct swap_info_struct *alloc_swap_info(void)
>  		plist_node_init(&p->avail_lists[i], 0);
>  	p->flags = SWP_USED;
>  	spin_unlock(&swap_lock);
> +	kvfree(tmp);
> +
>  	spin_lock_init(&p->lock);
>  	spin_lock_init(&p->cont_lock);
>  
>