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authorZhaoyang Huang <huangzhaoyang@gmail.com>2020-12-15 20:42:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-12-15 22:46:15 -0800
commitb50da6e9f42ade19141f6cf8870bb2312b055aa3 (patch)
treed504e2dec660733535ee66b19181cbde335b65c5 /mm/swapfile.c
parent489e9fea66f31086f85d9a18e61e4791d94a56a4 (diff)
mm: fix a race on nr_swap_pages
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>
Diffstat (limited to 'mm/swapfile.c')
-rw-r--r--mm/swapfile.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1c0a829f7311..9fffc5af29d1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1042,16 +1042,18 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
/* Only single cluster request supported */
WARN_ON_ONCE(n_goal > 1 && size == SWAPFILE_CLUSTER);
+ spin_lock(&swap_avail_lock);
+
avail_pgs = atomic_long_read(&nr_swap_pages) / size;
- if (avail_pgs <= 0)
+ if (avail_pgs <= 0) {
+ spin_unlock(&swap_avail_lock);
goto noswap;
+ }
n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
atomic_long_sub(n_goal * size, &nr_swap_pages);
- spin_lock(&swap_avail_lock);
-
start_over:
node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
@@ -1125,14 +1127,13 @@ swp_entry_t get_swap_page_of_type(int type)
spin_lock(&si->lock);
if (si->flags & SWP_WRITEOK) {
- atomic_long_dec(&nr_swap_pages);
/* This is called for allocating swap entry, not cache */
offset = scan_swap_map(si, 1);
if (offset) {
+ atomic_long_dec(&nr_swap_pages);
spin_unlock(&si->lock);
return swp_entry(type, offset);
}
- atomic_long_inc(&nr_swap_pages);
}
spin_unlock(&si->lock);
fail: