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| author | Zhaoyang Huang <huangzhaoyang@gmail.com> | 2020-12-15 20:42:23 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-12-15 22:46:15 -0800 |
| commit | b50da6e9f42ade19141f6cf8870bb2312b055aa3 (patch) | |
| tree | d504e2dec660733535ee66b19181cbde335b65c5 /mm | |
| parent | 489e9fea66f31086f85d9a18e61e4791d94a56a4 (diff) | |
| download | lwn-b50da6e9f42ade19141f6cf8870bb2312b055aa3.tar.gz lwn-b50da6e9f42ade19141f6cf8870bb2312b055aa3.zip | |
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')
| -rw-r--r-- | mm/swapfile.c | 11 |
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: |