linux-kernel - Re: 6.6.8 stable: crash in folio_mark

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Date: Mon,  1 Jan 2024 09:55:04 +0800
From: Hillf Danton <hdanton@...a.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Genes Lists <lists@...ience.com>,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: 6.6.8 stable: crash in folio_mark_dirty

On Sun, 31 Dec 2023 13:07:03 +0000 Matthew Wilcox <willy@...radead.org>
> On Sun, Dec 31, 2023 at 09:28:46AM +0800, Hillf Danton wrote:
> > On Sat, Dec 30, 2023 at 10:23:26AM -0500 Genes Lists <lists@...ience.com>
> > > Apologies in advance, but I cannot git bisect this since machine was
> > > running for 10 days on 6.6.8 before this happened.
> > >
> > > Dec 30 07:00:36 s6 kernel: ------------[ cut here ]------------
> > > Dec 30 07:00:36 s6 kernel: WARNING: CPU: 0 PID: 521524 at mm/page-writeback.c:2668 __folio_mark_dirty (??:?) 
> > > Dec 30 07:00:36 s6 kernel: CPU: 0 PID: 521524 Comm: rsync Not tainted 6.6.8-stable-1 #13 d238f5ab6a206cdb0cc5cd72f8688230f23d58df
> > > Dec 30 07:00:36 s6 kernel: block_dirty_folio (??:?) 
> > > Dec 30 07:00:36 s6 kernel: unmap_page_range (??:?) 
> > > Dec 30 07:00:36 s6 kernel: unmap_vmas (??:?) 
> > > Dec 30 07:00:36 s6 kernel: exit_mmap (??:?) 
> > > Dec 30 07:00:36 s6 kernel: __mmput (??:?) 
> > > Dec 30 07:00:36 s6 kernel: do_exit (??:?) 
> > > Dec 30 07:00:36 s6 kernel: do_group_exit (??:?) 
> > > Dec 30 07:00:36 s6 kernel: __x64_sys_exit_group (??:?) 
> > > Dec 30 07:00:36 s6 kernel: do_syscall_64 (??:?) 
> > 
> > See what comes out if race is handled.
> > Only for thoughts.
> 
> I don't think this can happen.  Look at the call trace;
> block_dirty_folio() is called from unmap_page_range().  That means the
> page is in the page tables.  We unmap the pages in a folio from the
> page tables before we set folio->mapping to NULL.  Look at
> invalidate_inode_pages2_range() for example:
> 
>                                 unmap_mapping_pages(mapping, indices[i],
>                                                 (1 + end - indices[i]), false);
>                         folio_lock(folio);
>                         folio_wait_writeback(folio);
>                         if (folio_mapped(folio))
>                                 unmap_mapping_folio(folio);
>                         BUG_ON(folio_mapped(folio));
>                                 if (!invalidate_complete_folio2(mapping, folio))
> 
What is missed here is the same check [1] in invalidate_inode_pages2_range(),
so I built no wheel.

			folio_lock(folio);
			if (unlikely(folio->mapping != mapping)) {
				folio_unlock(folio);
				continue;
			}

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/truncate.c#n658