Commit a9b80250 authored Aug 10, 2017 by Nadav Amit Committed by Linus Torvalds Aug 10, 2017

Revert "mm: numa: defer TLB flush for THP migration as long as possible"

While deferring TLB flushes is a good practice, the reverted patch
caused pending TLB flushes to be checked while the page-table lock is
not taken.  As a result, in architectures with weak memory model (PPC),
Linux may miss a memory-barrier, miss the fact TLB flushes are pending,
and cause (in theory) a memory corruption.

Since the alternative of using smp_mb__after_unlock_lock() was
considered a bit open-coded, and the performance impact is expected to
be small, the previous patch is reverted.

This reverts b0943d61 ("mm: numa: defer TLB flush for THP migration
as long as possible").

Link: http://lkml.kernel.org/r/20170802000818.4760-4-namit@vmware.com


Signed-off-by: Nadav Amit <namit@vmware.com>
Suggested-by: Mel Gorman <mgorman@suse.de>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 0a2c4048

mm/huge_memory.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -1495,6 +1495,13 @@ int do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
		goto clear_pmdnuma;
		}

		/*
		* The page_table_lock above provides a memory barrier
		* with change_protection_range.
		*/
		if (mm_tlb_flush_pending(vma->vm_mm))
		flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE);

		/*
		* Migrate the THP to the requested node, returns with page unlocked
		* and access rights restored.

mm/migrate.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -1937,12 +1937,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
		put_page(new_page);
		goto out_fail;
		}
		/*
		* We are not sure a pending tlb flush here is for a huge page
		* mapping or not. Hence use the tlb range variant
		*/
		if (mm_tlb_flush_pending(mm))
		flush_tlb_range(vma, mmun_start, mmun_end);

		/* Prepare a page as a migration target */
		__SetPageLocked(new_page);