The patch titled mm: improve page_lock_anon_vma() comment has been removed from the -mm tree. Its filename was mm-improve-page_lock_anon_vma-comment.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: mm: improve page_lock_anon_vma() comment From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> A slightly more verbose comment to go along with the trickery in page_lock_anon_vma(). Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Acked-by: Mel Gorman <mel@xxxxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: David Miller <davem@xxxxxxxxxxxxx> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> Cc: Russell King <rmk@xxxxxxxxxxxxxxxx> Cc: Paul Mundt <lethal@xxxxxxxxxxxx> Cc: Jeff Dike <jdike@xxxxxxxxxxx> Cc: Richard Weinberger <richard@xxxxxx> Cc: Tony Luck <tony.luck@xxxxxxxxx> Cc: Nick Piggin <npiggin@xxxxxxxxx> Cc: Namhyung Kim <namhyung@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/rmap.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff -puN mm/rmap.c~mm-improve-page_lock_anon_vma-comment mm/rmap.c --- a/mm/rmap.c~mm-improve-page_lock_anon_vma-comment +++ a/mm/rmap.c @@ -320,8 +320,22 @@ void __init anon_vma_init(void) } /* - * Getting a lock on a stable anon_vma from a page off the LRU is - * tricky: page_lock_anon_vma rely on RCU to guard against the races. + * Getting a lock on a stable anon_vma from a page off the LRU is tricky! + * + * Since there is no serialization what so ever against page_remove_rmap() + * the best this function can do is return a locked anon_vma that might + * have been relevant to this page. + * + * The page might have been remapped to a different anon_vma or the anon_vma + * returned may already be freed (and even reused). + * + * All users of this function must be very careful when walking the anon_vma + * chain and verify that the page in question is indeed mapped in it + * [ something equivalent to page_mapped_in_vma() ]. + * + * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap() + * that the anon_vma pointer from page->mapping is valid if there is a + * mapcount, we can dereference the anon_vma after observing those. */ struct anon_vma *page_lock_anon_vma(struct page *page) { _ Patches currently in -mm which might be from a.p.zijlstra@xxxxxxxxx are origin.patch linux-next.patch cpumask-convert-cpumask_of_cpu-to-cpumask_of.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html