Skip to content

mm/filemap: fix page end in filemap_get_read_batch

Nico Pache requested to merge npache/centos-stream-9:bz2181263.post into main 
commit 5956592ce337330cdff0399a6f8b6a5aea397a8e
Author: Qian Yingjin <qian@ddn.com>
Date:   Wed Feb 8 10:24:00 2023 +0800

    mm/filemap: fix page end in filemap_get_read_batch

    I was running traces of the read code against an RAID storage system to
    understand why read requests were being misaligned against the underlying
    RAID strips.  I found that the page end offset calculation in
    filemap_get_read_batch() was off by one.

    When a read is submitted with end offset 1048575, then it calculates the
    end page for read of 256 when it should be 255.  "last_index" is the index
    of the page beyond the end of the read and it should be skipped when get a
    batch of pages for read in @filemap_get_read_batch().

    The below simple patch fixes the problem.  This code was introduced in
    kernel 5.12.

    Link: https://lkml.kernel.org/r/20230208022400.28962-1-coolqyj@163.com
    Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read")
    Signed-off-by: Qian Yingjin <qian@ddn.com>
    Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2181263

Signed-off-by: Nico Pache npache@redhat.com

Merge request reports