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Filesystem DAX locking for 4.7

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- We use a bit in an exceptional radix tree entry as a lock bit and use it
   similarly to how page lock is used for normal faults.  This fixes races
   between hole instantiation and read faults of the same index.
 
 - Filesystem DAX PMD faults are disabled, and will be re-enabled when PMD
   locking is implemented.
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Merge tag 'dax-locking-for-4.7' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

Pull DAX locking updates from Ross Zwisler:
 "Filesystem DAX locking for 4.7

   - We use a bit in an exceptional radix tree entry as a lock bit and
     use it similarly to how page lock is used for normal faults.  This
     fixes races between hole instantiation and read faults of the same
     index.

   - Filesystem DAX PMD faults are disabled, and will be re-enabled when
     PMD locking is implemented"

* tag 'dax-locking-for-4.7' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  dax: Remove i_mmap_lock protection
  dax: Use radix tree entry lock to protect cow faults
  dax: New fault locking
  dax: Allow DAX code to replace exceptional entries
  dax: Define DAX lock bit for radix tree exceptional entry
  dax: Make huge page handling depend of CONFIG_BROKEN
  dax: Fix condition for filling of PMD holes
This commit is contained in:
Linus Torvalds 2016-05-26 20:00:28 -07:00
commit 478a1469a7
7 changed files with 514 additions and 236 deletions
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7
include/linux/mm.h
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@ -303,6 +303,12 @@ struct vm_fault {
* is set (which is also implied by
* VM_FAULT_ERROR).
*/
void *entry; /* ->fault handler can alternatively
* return locked DAX entry. In that
* case handler should return
* VM_FAULT_DAX_LOCKED and fill in
* entry here.
*/
/* for ->map_pages() only */
pgoff_t max_pgoff; /* map pages for offset from pgoff till
* max_pgoff inclusive */
@ -1076,6 +1082,7 @@ static inline void clear_page_pfmemalloc(struct page *page)
#define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */
#define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */
#define VM_FAULT_FALLBACK 0x0800 /* huge page fault failed, fall back to small */
#define VM_FAULT_DAX_LOCKED 0x1000 /* ->fault has locked DAX entry */
#define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */