diff options
| author | Huang Ying <ying.huang@intel.com> | 2018-04-23 08:20:28 +1000 |
|---|---|---|
| committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2018-04-23 08:23:48 +1000 |
| commit | 4536719200134075e89315ca0733f3b1b54b298b (patch) | |
| tree | 5092e17262e68b9766ce7909e1ee5bc2777d3b94 | |
| parent | a07fb3c26ee02e8811e8f1a626036b5cd010c7b2 (diff) | |
| download | linux-4536719200134075e89315ca0733f3b1b54b298b.tar.gz linux-4536719200134075e89315ca0733f3b1b54b298b.tar.xz | |
mm, swap: fix race between swapoff and some swap operations
- Add more comments to get_swap_device() to make it more clear about
possible swapoff or swapoff+swapon.
Link: http://lkml.kernel.org/r/20180223060010.954-1-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
| -rw-r--r-- | mm/memory.c | 2 | ||||
| -rw-r--r-- | mm/swapfile.c | 23 |
2 files changed, 24 insertions, 1 deletions
diff --git a/mm/memory.c b/mm/memory.c index 658a9da803c3..3b4e98f80b39 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2922,7 +2922,7 @@ int do_swap_page(struct vm_fault *vmf) struct swap_info_struct *si = swp_swap_info(entry); if (si->flags & SWP_SYNCHRONOUS_IO && - __swap_count(entry) == 1) { + __swap_count(entry) == 1) { /* skip swapcache */ page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address); diff --git a/mm/swapfile.c b/mm/swapfile.c index 5b9bb760532f..254a511c51d0 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1113,6 +1113,29 @@ static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry, * return pointer to swap_info_struct, and keep the swap entry valid * via preventing the swap device from being swapoff, until * put_swap_device() is called. Otherwise return NULL. + * + * Notice that swapoff or swapoff+swapon can still happen before the + * preempt_disable() in get_swap_device() or after the + * preempt_enable() in put_swap_device() if there isn't any other way + * to prevent swapoff, such as page lock, page table lock, etc. The + * caller must be prepared for that. For example, the following + * situation is possible. + * + * CPU1 CPU2 + * do_swap_page() + * ... swapoff+swapon + * __read_swap_cache_async() + * swapcache_prepare() + * __swap_duplicate() + * // check swap_map + * // verify PTE not changed + * + * In __swap_duplicate(), the swap_map need to be checked before + * changing partly because the specified swap entry may be for another + * swap device which has been swapoff. And in do_swap_page(), after + * the page is read from the swap device, the PTE is verified not + * changed with the page table locked to check whether the swap device + * has been swapoff or swapoff+swapon. */ struct swap_info_struct *get_swap_device(swp_entry_t entry) { |