Hi, Minchan, Minchan Kim <minchan@xxxxxxxxxx> writes: > Hi Huang, > > On Fri, Oct 27, 2017 at 01:53:27PM +0800, Huang, Ying wrote: >> From: Huang Ying <huang.ying.caritas@xxxxxxxxx> >> >> When a page fault occurs for a swap entry, the physical swap readahead >> (not the VMA base swap readahead) may readahead several swap entries >> after the fault swap entry. The readahead algorithm calculates some >> of the swap entries to readahead via increasing the offset of the >> fault swap entry without checking whether they are beyond the end of >> the swap device and it relys on the __swp_swapcount() and >> swapcache_prepare() to check it. Although __swp_swapcount() checks >> for the swap entry passed in, it will complain with the error message >> as follow for the expected invalid swap entry. This may make the end >> users confused. >> >> swap_info_get: Bad swap offset entry 0200f8a7 >> >> To fix the false error message, the swap entry checking is added in >> swap readahead to avoid to pass the out-bound swap entries and the >> swap entry reserved for the swap header to __swp_swapcount() and >> swapcache_prepare(). >> >> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> >> Cc: Minchan Kim <minchan@xxxxxxxxxx> >> Cc: Michal Hocko <mhocko@xxxxxxxx> >> Cc: <stable@xxxxxxxxxxxxxxx> # 4.11-4.13 >> Reported-by: Christian Kujau <lists@xxxxxxxxxxxxxxx> >> Fixes: e8c26ab60598 ("mm/swap: skip readahead for unreferenced swap slots") >> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> >> --- >> include/linux/swap.h | 1 + >> mm/swap_state.c | 6 ++++-- >> mm/swapfile.c | 21 +++++++++++++++++++++ >> 3 files changed, 26 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/swap.h b/include/linux/swap.h >> index 84255b3da7c1..43b4b821c805 100644 >> --- a/include/linux/swap.h >> +++ b/include/linux/swap.h >> @@ -476,6 +476,7 @@ extern int page_swapcount(struct page *); >> extern int __swap_count(struct swap_info_struct *si, swp_entry_t entry); >> extern int __swp_swapcount(swp_entry_t entry); >> extern int swp_swapcount(swp_entry_t entry); >> +extern bool swap_entry_check(swp_entry_t entry); >> extern struct swap_info_struct *page_swap_info(struct page *); >> extern struct swap_info_struct *swp_swap_info(swp_entry_t entry); >> extern bool reuse_swap_page(struct page *, int *); >> diff --git a/mm/swap_state.c b/mm/swap_state.c >> index 6c017ced11e6..7dd70e77058d 100644 >> --- a/mm/swap_state.c >> +++ b/mm/swap_state.c >> @@ -569,11 +569,13 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, >> /* Read a page_cluster sized and aligned cluster around offset. */ >> start_offset = offset & ~mask; >> end_offset = offset | mask; >> - if (!start_offset) /* First page is swap header. */ >> - start_offset++; >> >> blk_start_plug(&plug); >> for (offset = start_offset; offset <= end_offset ; offset++) { >> + swp_entry_t ent = swp_entry(swp_type(entry), offset); >> + >> + if (!swap_entry_check(ent)) >> + continue; >> /* Ok, do the async read-ahead now */ >> page = __read_swap_cache_async( >> swp_entry(swp_type(entry), offset), >> diff --git a/mm/swapfile.c b/mm/swapfile.c >> index 3074b02eaa09..b04cec29c234 100644 >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -1107,6 +1107,27 @@ static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry, >> return p; >> } >> >> +bool swap_entry_check(swp_entry_t entry) >> +{ >> + struct swap_info_struct *p; >> + unsigned long offset, type; >> + >> + type = swp_type(entry); >> + if (type >= nr_swapfiles) >> + goto bad_file; >> + p = swap_info[type]; >> + offset = swp_offset(entry); >> + if (unlikely(!offset || offset >= p->max)) >> + goto out; >> + >> + return true; >> + >> +bad_file: >> + pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val); >> +out: >> + return false; >> +} >> + >> static unsigned char __swap_entry_free(struct swap_info_struct *p, >> swp_entry_t entry, unsigned char usage) >> { >> -- >> 2.14.2 > > Although it's better than old, we can make it simple, still. > > diff --git a/include/linux/swapops.h b/include/linux/swapops.h > index 291c4b534658..f50d5a48f03a 100644 > --- a/include/linux/swapops.h > +++ b/include/linux/swapops.h > @@ -41,6 +41,13 @@ static inline unsigned swp_type(swp_entry_t entry) > return (entry.val >> SWP_TYPE_SHIFT(entry)); > } > > +extern struct swap_info_struct *swap_info[]; > + > +static inline struct swap_info_struct *swp_si(swp_entry_t entry) > +{ > + return swap_info[swp_type(entry)]; > +} > + Why not just use swp_swap_info()? > /* > * Extract the `offset' field from a swp_entry_t. The swp_entry_t is in > * arch-independent format > diff --git a/mm/swap_state.c b/mm/swap_state.c > index 378262d3a197..a0fe2d54ad09 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -554,6 +554,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, > struct vm_area_struct *vma, unsigned long addr) > { > struct page *page; > + struct swap_info_struct *si = swp_si(entry); > unsigned long entry_offset = swp_offset(entry); > unsigned long offset = entry_offset; > unsigned long start_offset, end_offset; > @@ -572,6 +573,9 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, > if (!start_offset) /* First page is swap header. */ > start_offset++; > > + if (end_offset >= si->max) > + end_offset = si->max - 1; > + I don't think two implementation has much difference. Both look OK for me. Best Regards, Huang, Ying > blk_start_plug(&plug); > for (offset = start_offset; offset <= end_offset ; offset++) { > /* Ok, do the async read-ahead now */