From: Matthew Wilcox <willy@infradead.org>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: Linux Memory Management List <linux-mm@kvack.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
vivek.kasireddy@intel.com,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: Large folios and filemap_get_folios_contig()
Date: Thu, 3 Apr 2025 13:35:48 +0100 [thread overview]
Message-ID: <Z-6ApNtjw9yvAGc4@casper.infradead.org> (raw)
In-Reply-To: <b714e4de-2583-4035-b829-72cfb5eb6fc6@gmx.com>
On Thu, Apr 03, 2025 at 08:06:53PM +1030, Qu Wenruo wrote:
> Recently I hit a bug when developing the large folios support for btrfs.
>
> That we call filemap_get_folios_contig(), then lock each returned folio.
> (We also have a case where we unlock each returned folio)
>
> However since a large folio can be returned several times in the batch,
> this obviously makes a deadlock, as btrfs is trying to lock the same
> folio more than once.
Sorry, what? A large folio should only be returned once. xas_next()
moves to the next folio. How is it possible that
filemap_get_folios_contig() returns the same folio more than once?
> Then I looked into the caller of filemap_get_folios_contig() inside
> mm/gup, and it indeed does the correct skip.
... that code looks wrong to me.
next prev parent reply other threads:[~2025-04-03 12:35 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-03 9:36 Large folios and filemap_get_folios_contig() Qu Wenruo
2025-04-03 12:35 ` Matthew Wilcox [this message]
2025-04-03 21:16 ` Qu Wenruo
2025-04-04 0:50 ` Vishal Moola (Oracle)
2025-04-04 4:15 ` Qu Wenruo
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