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dax: wrprotect pmd_t in dax_mapping_entry_mkclean 

Currently dax_mapping_entry_mkclean() fails to clean and write protect
the pmd_t of a DAX PMD entry during an *sync operation.  This can result
in data loss in the following sequence:

1) mmap write to DAX PMD, dirtying PMD radix tree entry and making the
   pmd_t dirty and writeable
2) fsync, flushing out PMD data and cleaning the radix tree entry. We
   currently fail to mark the pmd_t as clean and write protected.
3) more mmap writes to the PMD.  These don't cause any page faults since
   the pmd_t is dirty and writeable.  The radix tree entry remains clean.
4) fsync, which fails to flush the dirty PMD data because the radix tree
   entry was clean.
5) crash - dirty data that should have been fsync'd as part of 4) could
   still have been in the processor cache, and is lost.

Fix this by marking the pmd_t clean and write protected in
dax_mapping_entry_mkclean(), which is called as part of the fsync
operation 2).  This will cause the writes in step 3) above to generate
page faults where we'll re-dirty the PMD radix tree entry, resulting in
flushes in the fsync that happens in step 4).

Fixes: 4b4bb46d00 ("dax: clear dirty entry tags on cache flush")
Link: http://lkml.kernel.org/r/1482272586-21177-3-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ross Zwisler 2017-01-10 16:57:24 -08:00 committed by Linus Torvalds
parent 0979639595
commit f729c8c9b2
3 changed files with 38 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
fs/dax.c
View File

@ -691,8 +691,8 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping,
pgoff_t index, unsigned long pfn)
{
struct vm_area_struct *vma;
pte_t *ptep;
pte_t pte;
pte_t pte, *ptep = NULL;
pmd_t *pmdp = NULL;
spinlock_t *ptl;
bool changed;
@ -707,12 +707,32 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping,
address = pgoff_address(index, vma);
changed = false;
if (follow_pte(vma->vm_mm, address, &ptep, &ptl))
if (follow_pte_pmd(vma->vm_mm, address, &ptep, &pmdp, &ptl))
continue;
if (pmdp) {
#ifdef CONFIG_FS_DAX_PMD
pmd_t pmd;
if (pfn != pmd_pfn(*pmdp))
goto unlock_pmd;
if (!pmd_dirty(*pmdp) && !pmd_write(*pmdp))
goto unlock_pmd;
flush_cache_page(vma, address, pfn);
pmd = pmdp_huge_clear_flush(vma, address, pmdp);
pmd = pmd_wrprotect(pmd);
pmd = pmd_mkclean(pmd);
set_pmd_at(vma->vm_mm, address, pmdp, pmd);
changed = true;
unlock_pmd:
spin_unlock(ptl);
#endif
} else {
if (pfn != pte_pfn(*ptep))
goto unlock;
goto unlock_pte;
if (!pte_dirty(*ptep) && !pte_write(*ptep))
goto unlock;
goto unlock_pte;
flush_cache_page(vma, address, pfn);
pte = ptep_clear_flush(vma, address, ptep);
@ -720,8 +740,9 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping,
pte = pte_mkclean(pte);
set_pte_at(vma->vm_mm, address, ptep, pte);
changed = true;
unlock:
unlock_pte:
pte_unmap_unlock(ptep, ptl);
}
if (changed)
mmu_notifier_invalidate_page(vma->vm_mm, address);

2
include/linux/mm.h
View File

@ -1210,8 +1210,6 @@ int copy_page_range(struct mm_struct *dst, struct mm_struct *src,
struct vm_area_struct *vma);
void unmap_mapping_range(struct address_space *mapping,
loff_t const holebegin, loff_t const holelen, int even_cows);
int follow_pte(struct mm_struct *mm, unsigned long address, pte_t **ptepp,
spinlock_t **ptlp);
int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
int follow_pfn(struct vm_area_struct *vma, unsigned long address,

4
mm/memory.c
View File

@ -3819,8 +3819,8 @@ static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
return -EINVAL;
}
int follow_pte(struct mm_struct *mm, unsigned long address, pte_t **ptepp,
spinlock_t **ptlp)
static inline int follow_pte(struct mm_struct *mm, unsigned long address,
pte_t **ptepp, spinlock_t **ptlp)
{
int res;