From: Matthew Wilcox <willy@infradead.org>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Brown <broonie@kernel.org>, Linux-MM <linux-mm@kvack.org>
Subject: Re: shmem folio changes have broken linux-next
Date: Tue, 6 Aug 2024 16:16:42 +0100 [thread overview]
Message-ID: <ZrI-WqQIN7DGMOY2@casper.infradead.org> (raw)
In-Reply-To: <234b0b85-cbf1-4af4-85c9-ac0d00ceeed2@arm.com>
On Tue, Aug 06, 2024 at 09:47:19AM +0100, Ryan Roberts wrote:
> Our CI is reporting an oops during boot on linux-next (next-20240806) on arm64. Bisect tells me that it is due to your commit cdc4ad36a871b ("fs: Convert aops->write_begin to take a folio"), but there is no link to a mail thread on the patch and I can't find it in lore.
You're looking in the wrong place ;-)
https://lore.kernel.org/linux-fsdevel/20240717154716.237943-22-willy@infradead.org/#Z31mm:shmem.c
> Anyway, I believe the issue is that you are doing this in shmem_write_begin():
>
> if (folio_test_has_hwpoisoned(folio)) {
>
> But folio could be small and I think that function is only safe for large folios? (AFAICT it is unconditionally looking at the flags in the second page?).
>
> Elsewhere in the file, this pattern is used:
>
> if (folio_test_hwpoison(folio) ||
> (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) {
Ugh. The hwpoison stuff is too complicated. Because that's wrong too.
It should be ...
if (folio_test_large(folio) && folio_test_has_hwpoisoned(folio) ||
!folio_test_large(folio) && folio_test_hwpoison(folio))
right? But that's a mouthful to write. I'm tempted to rip it all out
and start again ...
> Here is the oops (pretty much as soon as we get into user space):
>
> [ 0.623253] page: refcount:3 mapcount:0 mapping:00000000eebcb8cf index:0x0 pfn:0x18cc07
> [ 0.624212] memcg:ffff000142023000
> [ 0.624617] aops:shmem_aops ino:800 dentry name:"memfd:snapd-env-generator"
> [ 0.625444] flags: 0xbfffe0000040005(locked|referenced|swapbacked|node=0|zone=2|lastcpupid=0x1ffff)
> [ 0.626532] raw: 0bfffe0000040005 0000000000000000 dead000000000122 ffff000181dd0ac0
> [ 0.627442] raw: 0000000000000000 0000000000000000 00000003ffffffff ffff000142023000
> [ 0.628331] page dumped because: VM_BUG_ON_PAGE(n > 0 && !((__builtin_constant_p(PG_head) && __builtin_constant_p((uintptr_t)(&page->flags) != (uintptr_t)((void *)0)) && (uintptr_t)(&page->flags) != (uintptr_t)((void *)0) && __builtin_constant_p(*(const unsigned long *)(&page->flags))) ? const_test_bit(PG_head, &page->flags) : generic_test_bit(PG_head, &page->flags)))
> [ 0.632106] ------------[ cut here ]------------
> [ 0.632630] kernel BUG at include/linux/page-flags.h:308!
I'm glad I made it so noisy instead of silently checking something
that's not the flag we thought it was ...
next prev parent reply other threads:[~2024-08-06 15:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-06 8:47 Ryan Roberts
2024-08-06 15:16 ` Matthew Wilcox [this message]
2024-08-06 15:29 ` Ryan Roberts
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