linux-kernel - [PATCH 0/1] RESEND fix page_cache_next/prev

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Date:   Fri,  2 Jun 2023 15:57:46 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Muchun Song <songmuchun@...edance.com>, vannapurve@...gle.com,
        erdemaktas@...gle.com, Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH 0/1] RESEND fix page_cache_next/prev_miss off by one error

In commits d0ce0e47b323 and 91a2fb956ad99, hugetlb code was changed to
use page_cache_next_miss to determine if a page was present in the page
cache.  However, the current implementation of page_cache_next_miss will
always return the passed index if max_scan is 1 as in the hugetlb code.
As a result, hugetlb code will always thing a page is present in the
cache, even if that is not the case.

The patch which follows addresses the issue by changing the implementation
of page_cache_next_miss and for consistency page_cache_prev_miss.  Since
such a patch also impacts the readahead code, I would suggest using the
patch by Sidhartha Kumar [1] to fix the issue in 6.3 and this patch moving
forward.

If we would rather not modify page_cache_next/prev_miss, then a new
interface as suggested by Ackerley Tng [2] could also be used.

Comments on the best way to fix moving forward would be appreciated.

[1] https://lore.kernel.org/linux-mm/20230505185301.534259-1-sidhartha.kumar@oracle.com/
[2] https://lore.kernel.org/linux-mm/98624c2f481966492b4eb8272aef747790229b73.1683069252.git.ackerleytng@google.com/

Mike Kravetz (1):
  page cache: fix page_cache_next/prev_miss off by one

 mm/filemap.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

-- 
2.40.1