mm: fix a race on nr_swap_pages
commit b50da6e9f4
upstream.
The scenario on which "Free swap = -4kB" happens in my system, which is caused
by several get_swap_pages racing with each other and show_swap_cache_info
happens simutaniously. No need to add a lock on get_swap_page_of_type as we
remove "Presub/PosAdd" here.
ProcessA ProcessB ProcessC
ngoals = 1 ngoals = 1
avail = nr_swap_pages(1) avail = nr_swap_pages(1)
nr_swap_pages(1) -= ngoals
nr_swap_pages(0) -= ngoals
nr_swap_pages = -1
Link: https://lkml.kernel.org/r/1607050340-4535-1-git-send-email-zhaoyang.huang@unisoc.com
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
pull/242/head^2
parent
c11f7749f1
commit
f472a59aa1
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@ -1045,16 +1045,18 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
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/* Only single cluster request supported */
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WARN_ON_ONCE(n_goal > 1 && size == SWAPFILE_CLUSTER);
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spin_lock(&swap_avail_lock);
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avail_pgs = atomic_long_read(&nr_swap_pages) / size;
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if (avail_pgs <= 0)
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if (avail_pgs <= 0) {
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spin_unlock(&swap_avail_lock);
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goto noswap;
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}
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n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
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atomic_long_sub(n_goal * size, &nr_swap_pages);
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spin_lock(&swap_avail_lock);
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start_over:
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node = numa_node_id();
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plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
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@ -1128,14 +1130,13 @@ swp_entry_t get_swap_page_of_type(int type)
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spin_lock(&si->lock);
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if (si->flags & SWP_WRITEOK) {
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atomic_long_dec(&nr_swap_pages);
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/* This is called for allocating swap entry, not cache */
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offset = scan_swap_map(si, 1);
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if (offset) {
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atomic_long_dec(&nr_swap_pages);
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spin_unlock(&si->lock);
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return swp_entry(type, offset);
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}
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atomic_long_inc(&nr_swap_pages);
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}
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spin_unlock(&si->lock);
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fail:
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