From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
William Kucharski <william.kucharski@oracle.com>,
Christoph Hellwig <hch@lst.de>,
Mike Rapoport <rppt@linux.ibm.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH] mm: delete unsafe BUG from page_cache_add_speculative()
Date: Thu, 9 Dec 2021 12:30:16 +0300 [thread overview]
Message-ID: <20211209093016.eivzxmgr6c4twmus@black.fi.intel.com> (raw)
In-Reply-To: <8b98fc6f-3439-8614-c3f3-945c659a1aba@google.com>
On Wed, Dec 08, 2021 at 11:19:18PM -0800, Hugh Dickins wrote:
> It is not easily reproducible, but on 5.16-rc I have several times hit
> the VM_BUG_ON_PAGE(PageTail(page), page) in page_cache_add_speculative():
> usually from filemap_get_read_batch() for an ext4 read, yesterday from
> next_uptodate_page() from filemap_map_pages() for a shmem fault.
>
> That BUG used to be placed where page_ref_add_unless() had succeeded,
> but now it is placed before folio_ref_add_unless() is attempted: that
> is not safe, since it is only the acquired reference which makes the
> page safe from racing THP collapse or split.
>
> We could keep the BUG, checking PageTail only when folio_ref_try_add_rcu()
> has succeeded; but I don't think it adds much value - just delete it.
>
> Fixes: 020853b6f5ea ("mm: Add folio_try_get_rcu()")
> Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2021-12-09 9:30 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-09 7:19 [PATCH] mm: delete unsafe BUG from page_cache_add_speculative() Hugh Dickins
2021-12-09 9:30 ` Kirill A. Shutemov [this message]
2021-12-09 13:55 ` Matthew Wilcox
2021-12-10 17:20 ` Andrew Morton
2021-12-10 19:18 ` Hugh Dickins
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