• Hugh Dickins's avatar
    osd fs: __r4w_get_page rely on PageUptodate for uptodate · 3066a967
    Hugh Dickins authored
    Commit 42cb14b1 ("mm: migrate dirty page without
    clear_page_dirty_for_io etc") simplified the migration of a PageDirty
    pagecache page: one stat needs moving from zone to zone and that's about
    all.
    
    It's convenient and safest for it to shift the PageDirty bit from old
    page to new, just before updating the zone stats: before copying data
    and marking the new PageUptodate.  This is all done while both pages are
    isolated and locked, just as before; and just as before, there's a
    moment when the new page is visible in the radix_tree, but not yet
    PageUptodate.  What's new is that it may now be briefly visible as
    PageDirty before it is PageUptodate.
    
    When I scoured the tree to see if this could cause a problem anywhere,
    the only places I found were in two similar functions __r4w_get_page():
    which look up a page with find_get_page() (not using page lock), then
    claim it's uptodate if it's PageDirty or PageWriteback or PageUptodate.
    
    I'm not sure whether that was right before, but now it might be wrong
    (on rare occasions): only claim the page is uptodate if PageUptodate.
    Or perhaps the page in question could never be migratable anyway?
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Tested-by: default avatarBoaz Harrosh <ooo@electrozaur.com>
    Cc: Benny Halevy <bhalevy@panasas.com>
    Cc: Trond Myklebust <trond.myklebust@primarydata.com>
    Cc: Christoph Lameter <cl@linux.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3066a967
inode.c 36.7 KB