Re: [PATCH V1] fuse: Remove __GFP_FS flag to avoid allocator recursing

[ppvk@codeaurora.org]

On 2020-09-14 19:37, Matthew Wilcox wrote:
> On Mon, Sep 14, 2020 at 07:26:15PM +0530, Pradeep P V K wrote:
>> Process#1(kswapd) held an inode lock and initaited a writeback to free
>> the pages, as the inode superblock is fuse, process#2 forms a fuse
>> request. Process#3 (Fuse daemon threads) while serving process#2 
>> request,
>> it requires memory(pages) and as the system is already running in low
>> memory it ends up in calling try_to_ free_pages(), which might now 
>> call
>> kswapd again, which is already stuck with an inode lock held. Thus 
>> forms
>> a deadlock.
>> 
>> So, remove __GFP_FS flag to avoid allocator recursing into the
>> filesystem that might already held locks.
> 
> This is the wrong way to fix the problem.  The fuse daemon threads 
> should
> have called memalloc_nofs_save() as this prevents them from 
> inadvertently
> tripping over other places where they forgot to use GFP_NOFS (or have
> no way to pass a GFP_NOFS flags argument).

Thanks Matthew for pointing this. I will address this in my next patch 
set.

Thanks and Regards,
Pradeep