From: Mel Gorman <mgor...@suse.de>
commit 1ad9f620c3a22fa800489455ce517c29e576934e upstream
Sasha reported the following bug using trinity
kernel BUG at mm/mprotect.c:149!
invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 20 PID: 26219 Comm: trinity-c216 Tainted: G W
3.14.0-rc5-next-20140305-sasha-00011-ge06f5f3-dirty #105
task: ffff8800b6c80000 ti: ffff880228436000 task.ti: ffff880228436000
RIP: change_protection_range+0x3b3/0x500
Call Trace:
change_protection+0x25/0x30
change_prot_numa+0x1b/0x30
task_numa_work+0x279/0x360
task_work_run+0xae/0xf0
do_notify_resume+0x8e/0xe0
retint_signal+0x4d/0x92
The VM_BUG_ON was added in -mm 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.
Signed-off-by: Mel Gorman <mgor...@suse.de>
Reported-by: Sasha Levin <sasha.le...@oracle.com>
Reviewed-by: Rik van Riel <r...@redhat.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Yang Shi <yang....@windriver.com>
---
mm/mprotect.c | 36 ++++++++++++++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2afc40e..c43d557 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -36,6 +36,34 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot,
pgprot_t newprot)
}
#endif
+/*
+ * 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. This
+ * function checks for a transhuge pmd under the appropriate lock. It
+ * returns a pte if it was successfully locked or NULL if it raced with
+ * a transhuge insertion.
+ */
+static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long addr, int prot_numa, spinlock_t **ptl)
+{
+ pte_t *pte;
+ spinlock_t *pmdl;
+
+ /* !prot_numa is protected by mmap_sem held for write */
+ if (!prot_numa)
+ return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
+
+ pmdl = pmd_lock(vma->vm_mm, pmd);
+ if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
+ spin_unlock(pmdl);
+ return NULL;
+ }
+
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
+ spin_unlock(pmdl);
+ return pte;
+}
+
static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
@@ -45,7 +73,10 @@ static unsigned long change_pte_range(struct vm_area_struct
*vma, pmd_t *pmd,
spinlock_t *ptl;
unsigned long pages = 0;
- pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
+ if (!pte)
+ return 0;
+
arch_enter_lazy_mmu_mode();
do {
oldpte = *pte;
@@ -141,12 +172,13 @@ 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;
--
2.0.2
--
_______________________________________________
linux-yocto mailing list
linux-yocto@yoctoproject.org
https://lists.yoctoproject.org/listinfo/linux-yocto
