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

[Joseph Qi <joseph.qi@linux.alibaba.com>]

Hi,

On 19/1/29 16:53, Aaron Lu wrote:
> 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.
> 
avail_lists in swap_info_struct is dynamic allocated.
So if we use back kzalloc/kfree, how to deal with the case that
nr_node_ids is big?

Thanks,
Joseph

> 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);
>>  
>>