[PATCH] mm: numa: Recheck for transhuge pages under lock during protection changes
From: Mel Gorman
Date: Wed Mar 12 2014 - 06:36:17 EST
Andrew, this should go with the patches
mmnuma-reorganize-change_pmd_range.patch
mmnuma-reorganize-change_pmd_range-fix.patch
move-mmu-notifier-call-from-change_protection-to-change_pmd_range.patch
in mmotm please.
Thanks.
---8<---
From: Mel Gorman <mgorman@xxxxxxx>
Subject: [PATCH] mm: numa: Recheck for transhuge pages under lock during protection changes
Sasha Levin reported the following bug using trinity
[ 886.745765] kernel BUG at mm/mprotect.c:149!
[ 886.746831] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 886.748511] Dumping ftrace buffer:
[ 886.749998] (ftrace buffer empty)
[ 886.750110] Modules linked in:
[ 886.751396] CPU: 20 PID: 26219 Comm: trinity-c216 Tainted: G W 3.14.0-rc5-next-20140305-sasha-00011-ge06f5f3-dirty #105
[ 886.751396] task: ffff8800b6c80000 ti: ffff880228436000 task.ti: ffff880228436000
[ 886.751396] RIP: 0010:[<ffffffff812aab33>] [<ffffffff812aab33>] change_protection_range+0x3b3/0x500
[ 886.751396] RSP: 0000:ffff880228437da8 EFLAGS: 00010282
[ 886.751396] RAX: 8000000527c008e5 RBX: 00007f647916e000 RCX: 0000000000000000
[ 886.751396] RDX: ffff8802ef488e40 RSI: 00007f6479000000 RDI: 8000000527c008e5
[ 886.751396] RBP: ffff880228437e78 R08: 0000000000000000 R09: 0000000000000000
[ 886.751396] R10: 0000000000000001 R11: 0000000000000000 R12: ffff8802ef488e40
[ 886.751396] R13: 00007f6479000000 R14: 00007f647916e000 R15: 00007f646e34e000
[ 886.751396] FS: 00007f64b28d4700(0000) GS:ffff88052ba00000(0000) knlGS:0000000000000000
[ 886.751396] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 886.751396] CR2: 00007f64aed83af8 CR3: 0000000206e52000 CR4: 00000000000006a0
[ 886.751396] Stack:
[ 886.751396] ffff880200000001 ffffffff8447f152 ffff880228437dd8 ffff880228af3000
[ 886.769142] 00007f646e34e000 00007f647916dfff 0000000000000000 00007f647916e000
[ 886.769142] ffff880206e527f0 00007f647916dfff 0000000000000000 0000000000000000
[ 886.769142] Call Trace:
[ 886.769142] [<ffffffff8447f152>] ? preempt_count_sub+0xe2/0x120
[ 886.769142] [<ffffffff812aaca5>] change_protection+0x25/0x30
[ 886.769142] [<ffffffff812c3eeb>] change_prot_numa+0x1b/0x30
[ 886.769142] [<ffffffff8118df49>] task_numa_work+0x279/0x360
[ 886.769142] [<ffffffff8116c57e>] task_work_run+0xae/0xf0
[ 886.769142] [<ffffffff8106ffbe>] do_notify_resume+0x8e/0xe0
[ 886.769142] [<ffffffff8447a93b>] retint_signal+0x4d/0x92
[ 886.769142] Code: 49 8b 3c 24 48 83 3d fc 2e ba 04 00 75 12 0f 0b 0f 1f 84 00 00 00 00 00 eb fe 66 0f 1f 44 00 00 48 89 f8 66 66 66 90 84 c0 79 0d <0f> 0b 0f 1f 00 eb fe 66 0f 1f 44 00 00 8b 4d 9c 44 8b 4d 98
+89
[ 886.769142] RIP [<ffffffff812aab33>] change_protection_range+0x3b3/0x500
[ 886.769142] RSP <ffff880228437da8>
The VM_BUG_ON was added by the patch "mm,numa: reorganize
change_pmd_range". The race existed without the patch but was just harder
to hit.
The problem is that a transhuge check is made without holding the PTL. It's
possible at the time of the check that a parallel fault clears the pmd
and inserts a new one which then triggers the VM_BUG_ON check. This patch
removes the VM_BUG_ON but fixes the race by rechecking transhuge under the
PTL when marking page tables for NUMA hinting and bailing if a race occurred.
It is not a problem for calls to mprotect() as they hold mmap_sem for write.
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/mprotect.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2afc40e..72061a2 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -46,6 +46,17 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long pages = 0;
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+
+ /*
+ * For a prot_numa update we only hold mmap_sem for read so there is a
+ * potential race with faulting where a pmd was temporarily none so
+ * recheck it under the lock and bail if we race
+ */
+ if (prot_numa && unlikely(pmd_trans_huge(*pmd))) {
+ pte_unmap_unlock(pte, ptl);
+ return 0;
+ }
+
arch_enter_lazy_mmu_mode();
do {
oldpte = *pte;
@@ -141,12 +152,13 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
pages += HPAGE_PMD_NR;
nr_huge_updates++;
}
+
+ /* huge pmd was handled */
continue;
}
}
/* fall through, the trans huge pmd just split */
}
- VM_BUG_ON(pmd_trans_huge(*pmd));
this_pages = change_pte_range(vma, pmd, addr, next, newprot,
dirty_accountable, prot_numa);
pages += this_pages;
--
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