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https://github.com/team-infusion-developers/android_kernel_samsung_msm8976.git
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cbab0e4eec
read_swap_cache_async() can race against get_swap_page(), and stumble across a SWAP_HAS_CACHE entry in the swap map whose page wasn't brought into the swapcache yet. This transient swap_map state is expected to be transitory, but the actual placement of discard at scan_swap_map() inserts a wait for I/O completion thus making the thread at read_swap_cache_async() to loop around its -EEXIST case, while the other end at get_swap_page() is scheduled away at scan_swap_map(). This can leave the system deadlocked if the I/O completion happens to be waiting on the CPU waitqueue where read_swap_cache_async() is busy looping and !CONFIG_PREEMPT. This patch introduces a cond_resched() call to make the aforementioned read_swap_cache_async() busy loop condition to bail out when necessary, thus avoiding the subtle race window. Signed-off-by: Rafael Aquini <aquini@redhat.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Shaohua Li <shli@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
439 lines
11 KiB
C
439 lines
11 KiB
C
/*
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* linux/mm/swap_state.c
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*
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* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
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* Swap reorganised 29.12.95, Stephen Tweedie
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*
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* Rewritten to use page cache, (C) 1998 Stephen Tweedie
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*/
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#include <linux/mm.h>
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#include <linux/gfp.h>
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#include <linux/kernel_stat.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/init.h>
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#include <linux/pagemap.h>
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#include <linux/backing-dev.h>
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#include <linux/blkdev.h>
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#include <linux/pagevec.h>
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#include <linux/migrate.h>
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#include <linux/page_cgroup.h>
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#include <asm/pgtable.h>
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/*
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* swapper_space is a fiction, retained to simplify the path through
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* vmscan's shrink_page_list.
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*/
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static const struct address_space_operations swap_aops = {
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.writepage = swap_writepage,
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.set_page_dirty = swap_set_page_dirty,
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.migratepage = migrate_page,
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};
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static struct backing_dev_info swap_backing_dev_info = {
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.name = "swap",
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.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
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};
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struct address_space swapper_spaces[MAX_SWAPFILES] = {
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[0 ... MAX_SWAPFILES - 1] = {
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.page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
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.a_ops = &swap_aops,
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.backing_dev_info = &swap_backing_dev_info,
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}
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};
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#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
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static struct {
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unsigned long add_total;
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unsigned long del_total;
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unsigned long find_success;
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unsigned long find_total;
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} swap_cache_info;
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unsigned long total_swapcache_pages(void)
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{
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int i;
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unsigned long ret = 0;
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for (i = 0; i < MAX_SWAPFILES; i++)
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ret += swapper_spaces[i].nrpages;
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return ret;
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}
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void show_swap_cache_info(void)
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{
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printk("%lu pages in swap cache\n", total_swapcache_pages());
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printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
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swap_cache_info.add_total, swap_cache_info.del_total,
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swap_cache_info.find_success, swap_cache_info.find_total);
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printk("Free swap = %ldkB\n",
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get_nr_swap_pages() << (PAGE_SHIFT - 10));
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printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
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}
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/*
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* __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
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* but sets SwapCache flag and private instead of mapping and index.
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*/
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int __add_to_swap_cache(struct page *page, swp_entry_t entry)
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{
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int error;
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struct address_space *address_space;
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(PageSwapCache(page));
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VM_BUG_ON(!PageSwapBacked(page));
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page_cache_get(page);
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SetPageSwapCache(page);
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set_page_private(page, entry.val);
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address_space = swap_address_space(entry);
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spin_lock_irq(&address_space->tree_lock);
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error = radix_tree_insert(&address_space->page_tree,
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entry.val, page);
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if (likely(!error)) {
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address_space->nrpages++;
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__inc_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(add_total);
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}
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spin_unlock_irq(&address_space->tree_lock);
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if (unlikely(error)) {
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/*
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* Only the context which have set SWAP_HAS_CACHE flag
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* would call add_to_swap_cache().
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* So add_to_swap_cache() doesn't returns -EEXIST.
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*/
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VM_BUG_ON(error == -EEXIST);
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set_page_private(page, 0UL);
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ClearPageSwapCache(page);
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page_cache_release(page);
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}
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return error;
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}
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int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
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{
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int error;
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error = radix_tree_preload(gfp_mask);
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if (!error) {
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error = __add_to_swap_cache(page, entry);
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radix_tree_preload_end();
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}
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return error;
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}
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/*
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* This must be called only on pages that have
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* been verified to be in the swap cache.
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*/
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void __delete_from_swap_cache(struct page *page)
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{
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swp_entry_t entry;
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struct address_space *address_space;
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(!PageSwapCache(page));
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VM_BUG_ON(PageWriteback(page));
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entry.val = page_private(page);
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address_space = swap_address_space(entry);
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radix_tree_delete(&address_space->page_tree, page_private(page));
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set_page_private(page, 0);
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ClearPageSwapCache(page);
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address_space->nrpages--;
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__dec_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(del_total);
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}
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/**
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* add_to_swap - allocate swap space for a page
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* @page: page we want to move to swap
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*
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* Allocate swap space for the page and add the page to the
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* swap cache. Caller needs to hold the page lock.
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*/
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int add_to_swap(struct page *page, struct list_head *list)
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{
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swp_entry_t entry;
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int err;
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(!PageUptodate(page));
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entry = get_swap_page();
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if (!entry.val)
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return 0;
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if (unlikely(PageTransHuge(page)))
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if (unlikely(split_huge_page_to_list(page, list))) {
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swapcache_free(entry, NULL);
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return 0;
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}
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/*
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* Radix-tree node allocations from PF_MEMALLOC contexts could
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* completely exhaust the page allocator. __GFP_NOMEMALLOC
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* stops emergency reserves from being allocated.
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*
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* TODO: this could cause a theoretical memory reclaim
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* deadlock in the swap out path.
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*/
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/*
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* Add it to the swap cache and mark it dirty
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*/
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err = add_to_swap_cache(page, entry,
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__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
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if (!err) { /* Success */
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SetPageDirty(page);
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return 1;
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} else { /* -ENOMEM radix-tree allocation failure */
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/*
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* add_to_swap_cache() doesn't return -EEXIST, so we can safely
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* clear SWAP_HAS_CACHE flag.
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*/
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swapcache_free(entry, NULL);
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return 0;
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}
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}
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/*
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* This must be called only on pages that have
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* been verified to be in the swap cache and locked.
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* It will never put the page into the free list,
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* the caller has a reference on the page.
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*/
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void delete_from_swap_cache(struct page *page)
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{
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swp_entry_t entry;
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struct address_space *address_space;
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entry.val = page_private(page);
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address_space = swap_address_space(entry);
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spin_lock_irq(&address_space->tree_lock);
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__delete_from_swap_cache(page);
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spin_unlock_irq(&address_space->tree_lock);
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swapcache_free(entry, page);
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page_cache_release(page);
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}
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/*
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* If we are the only user, then try to free up the swap cache.
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*
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* Its ok to check for PageSwapCache without the page lock
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* here because we are going to recheck again inside
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* try_to_free_swap() _with_ the lock.
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* - Marcelo
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*/
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static inline void free_swap_cache(struct page *page)
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{
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if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
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try_to_free_swap(page);
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unlock_page(page);
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}
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}
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/*
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* Perform a free_page(), also freeing any swap cache associated with
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* this page if it is the last user of the page.
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*/
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void free_page_and_swap_cache(struct page *page)
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{
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free_swap_cache(page);
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page_cache_release(page);
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}
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/*
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* Passed an array of pages, drop them all from swapcache and then release
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* them. They are removed from the LRU and freed if this is their last use.
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*/
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void free_pages_and_swap_cache(struct page **pages, int nr)
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{
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struct page **pagep = pages;
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lru_add_drain();
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while (nr) {
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int todo = min(nr, PAGEVEC_SIZE);
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int i;
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for (i = 0; i < todo; i++)
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free_swap_cache(pagep[i]);
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release_pages(pagep, todo, 0);
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pagep += todo;
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nr -= todo;
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}
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}
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/*
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* Lookup a swap entry in the swap cache. A found page will be returned
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* unlocked and with its refcount incremented - we rely on the kernel
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* lock getting page table operations atomic even if we drop the page
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* lock before returning.
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*/
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struct page * lookup_swap_cache(swp_entry_t entry)
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{
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struct page *page;
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page = find_get_page(swap_address_space(entry), entry.val);
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if (page)
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INC_CACHE_INFO(find_success);
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INC_CACHE_INFO(find_total);
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return page;
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}
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/*
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* Locate a page of swap in physical memory, reserving swap cache space
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* and reading the disk if it is not already cached.
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* A failure return means that either the page allocation failed or that
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* the swap entry is no longer in use.
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*/
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struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
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struct vm_area_struct *vma, unsigned long addr)
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{
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struct page *found_page, *new_page = NULL;
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int err;
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do {
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/*
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* First check the swap cache. Since this is normally
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* called after lookup_swap_cache() failed, re-calling
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* that would confuse statistics.
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*/
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found_page = find_get_page(swap_address_space(entry),
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entry.val);
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if (found_page)
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break;
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/*
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* Get a new page to read into from swap.
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*/
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if (!new_page) {
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new_page = alloc_page_vma(gfp_mask, vma, addr);
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if (!new_page)
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break; /* Out of memory */
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}
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/*
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* call radix_tree_preload() while we can wait.
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*/
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err = radix_tree_preload(gfp_mask & GFP_KERNEL);
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if (err)
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break;
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/*
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* Swap entry may have been freed since our caller observed it.
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*/
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err = swapcache_prepare(entry);
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if (err == -EEXIST) {
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radix_tree_preload_end();
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/*
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* We might race against get_swap_page() and stumble
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* across a SWAP_HAS_CACHE swap_map entry whose page
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* has not been brought into the swapcache yet, while
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* the other end is scheduled away waiting on discard
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* I/O completion at scan_swap_map().
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*
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* In order to avoid turning this transitory state
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* into a permanent loop around this -EEXIST case
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* if !CONFIG_PREEMPT and the I/O completion happens
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* to be waiting on the CPU waitqueue where we are now
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* busy looping, we just conditionally invoke the
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* scheduler here, if there are some more important
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* tasks to run.
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*/
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cond_resched();
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continue;
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}
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if (err) { /* swp entry is obsolete ? */
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radix_tree_preload_end();
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break;
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}
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/* May fail (-ENOMEM) if radix-tree node allocation failed. */
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__set_page_locked(new_page);
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SetPageSwapBacked(new_page);
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err = __add_to_swap_cache(new_page, entry);
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if (likely(!err)) {
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radix_tree_preload_end();
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/*
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* Initiate read into locked page and return.
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*/
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lru_cache_add_anon(new_page);
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swap_readpage(new_page);
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return new_page;
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}
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radix_tree_preload_end();
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ClearPageSwapBacked(new_page);
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__clear_page_locked(new_page);
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/*
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* add_to_swap_cache() doesn't return -EEXIST, so we can safely
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* clear SWAP_HAS_CACHE flag.
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*/
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swapcache_free(entry, NULL);
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} while (err != -ENOMEM);
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if (new_page)
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page_cache_release(new_page);
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return found_page;
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}
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/**
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* swapin_readahead - swap in pages in hope we need them soon
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* @entry: swap entry of this memory
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* @gfp_mask: memory allocation flags
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* @vma: user vma this address belongs to
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* @addr: target address for mempolicy
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*
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* Returns the struct page for entry and addr, after queueing swapin.
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*
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* Primitive swap readahead code. We simply read an aligned block of
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* (1 << page_cluster) entries in the swap area. This method is chosen
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* because it doesn't cost us any seek time. We also make sure to queue
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* the 'original' request together with the readahead ones...
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*
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* This has been extended to use the NUMA policies from the mm triggering
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* the readahead.
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*
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* Caller must hold down_read on the vma->vm_mm if vma is not NULL.
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*/
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struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
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struct vm_area_struct *vma, unsigned long addr)
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{
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struct page *page;
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unsigned long offset = swp_offset(entry);
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unsigned long start_offset, end_offset;
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unsigned long mask = (1UL << page_cluster) - 1;
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struct blk_plug plug;
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/* Read a page_cluster sized and aligned cluster around offset. */
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start_offset = offset & ~mask;
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end_offset = offset | mask;
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if (!start_offset) /* First page is swap header. */
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start_offset++;
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blk_start_plug(&plug);
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for (offset = start_offset; offset <= end_offset ; offset++) {
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/* Ok, do the async read-ahead now */
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page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
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gfp_mask, vma, addr);
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if (!page)
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continue;
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page_cache_release(page);
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}
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blk_finish_plug(&plug);
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lru_add_drain(); /* Push any new pages onto the LRU now */
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return read_swap_cache_async(entry, gfp_mask, vma, addr);
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}
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