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Message-ID: <Z-6cS9Cg1eN0w6XL@tiehlicka>
Date: Thu, 3 Apr 2025 16:33:47 +0200
From: Michal Hocko <mhocko@...e.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Matt Fleming <matt@...dmodwrite.com>, willy@...radead.org,
adilger.kernel@...ger.ca, akpm@...ux-foundation.org,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
luka.2016.cs@...il.com, tytso@....edu,
Barry Song <baohua@...nel.org>, kernel-team@...udflare.com,
Miklos Szeredi <miklos@...redi.hu>,
Amir Goldstein <amir73il@...il.com>,
Dave Chinner <david@...morbit.com>,
Qi Zheng <zhengqi.arch@...edance.com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Muchun Song <muchun.song@...ux.dev>
Subject: Re: Potential Linux Crash: WARNING in ext4_dirty_folio in Linux
kernel v6.13-rc5
On Thu 03-04-25 14:58:25, Vlastimil Babka wrote:
> On 4/3/25 14:29, Matt Fleming wrote:
> > On Wed, Mar 26, 2025 at 10:59 AM Matt Fleming <matt@...dmodwrite.com> wrote:
> >>
> >> Hi there,
>
> + Cc also Michal
>
> >> I'm also seeing this PF_MEMALLOC WARN triggered from kswapd in 6.12.19.
>
> We're talking about __alloc_pages_slowpath() doing WARN_ON_ONCE(current-
> >flags & PF_MEMALLOC); for __GFP_NOFAIL allocations.
>
> kswapd() sets:
>
> tsk->flags |= PF_MEMALLOC | PF_KSWAPD;
>
> so any __GFP_NOFAIL allocation done in the kswapd context risks this
> warning. It's also objectively bad IMHO because for direct reclaim we can
> loop and hope kswapd rescues us, but kswapd would then have to rely on
> direct reclaimers to get unstuck. I don't see an easy generic solution?
Right. I do not think NOFAIL request from the reclaim context is really
something we can commit to support. This really needs to be addressed on
the shrinker side.
> >> Does overlayfs need some kind of background inode reclaim support?
> >
> > Hey everyone, I know there was some off-list discussion last week at
> > LSFMM, but I don't think a definite solution has been proposed for the
> > below stacktrace.
> >
> > What is the shrinker API policy wrt memory allocation and I/O? Should
> > overlayfs do something more like XFS and background reclaim to avoid
> > GFP_NOFAIL
> > allocations when kswapd is shrinking caches?
> >
> >> Call Trace:
> >> <TASK>
> >> __alloc_pages_noprof+0x31c/0x330
> >> alloc_pages_mpol_noprof+0xe3/0x1d0
> >> folio_alloc_noprof+0x5b/0xa0
> >> __filemap_get_folio+0x1f3/0x380
> >> __getblk_slow+0xa3/0x1e0
> >> __ext4_get_inode_loc+0x121/0x4b0
> >> ext4_get_inode_loc+0x40/0xa0
> >> ext4_reserve_inode_write+0x39/0xc0
> >> __ext4_mark_inode_dirty+0x5b/0x220
> >> ext4_evict_inode+0x26d/0x690
> >> evict+0x112/0x2a0
> >> __dentry_kill+0x71/0x180
> >> dput+0xeb/0x1b0
> >> ovl_stack_put+0x2e/0x50 [overlay]
> >> ovl_destroy_inode+0x3a/0x60 [overlay]
> >> destroy_inode+0x3b/0x70
> >> __dentry_kill+0x71/0x180
> >> shrink_dentry_list+0x6b/0xe0
> >> prune_dcache_sb+0x56/0x80
> >> super_cache_scan+0x12c/0x1e0
> >> do_shrink_slab+0x13b/0x350
> >> shrink_slab+0x278/0x3a0
> >> shrink_node+0x328/0x880
> >> balance_pgdat+0x36d/0x740
> >> kswapd+0x1f0/0x380
> >> kthread+0xd2/0x100
> >> ret_from_fork+0x34/0x50
> >> ret_from_fork_asm+0x1a/0x30
> >> </TASK>
> >
--
Michal Hocko
SUSE Labs
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