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| author | Yu Zhao <yuzhao@google.com> | 2021-06-30 18:49:48 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-06-30 20:47:28 -0700 |
| commit | 2d2b8d2b67713da5de333a8849342503a9f21c60 (patch) | |
| tree | 927354b2ae89b6814e6abb59de6f5f0b27945c97 /mm/vmscan.c | |
| parent | 4a8f021ba0a220a95d4251ea3f199ef693f1249b (diff) | |
| download | lwn-2d2b8d2b67713da5de333a8849342503a9f21c60.tar.gz lwn-2d2b8d2b67713da5de333a8849342503a9f21c60.zip | |
mm/vmscan.c: fix potential deadlock in reclaim_pages()
Theoretically without the protect from memalloc_noreclaim_save() and
memalloc_noreclaim_restore(), reclaim_pages() can go into the block
I/O layer recursively and deadlock.
Querying 'reclaim_pages' in our kernel crash databases didn't yield
any results. So the deadlock seems unlikely to happen. A possible
explanation is that the only user of reclaim_pages(), i.e.,
MADV_PAGEOUT, is usually called before memory pressure builds up,
e.g., on Android and Chrome OS. Under such a condition, allocations in
the block I/O layer can be fulfilled without diverting to direct
reclaim and therefore the recursion is avoided.
Link: https://lkml.kernel.org/r/20210622074642.785473-1-yuzhao@google.com
Link: https://lkml.kernel.org/r/20210614194727.2684053-1-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
| -rw-r--r-- | mm/vmscan.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c index d7c3cb8688dd..7b52ab166aae 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1701,6 +1701,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, unsigned int nr_reclaimed; struct page *page, *next; LIST_HEAD(clean_pages); + unsigned int noreclaim_flag; list_for_each_entry_safe(page, next, page_list, lru) { if (!PageHuge(page) && page_is_file_lru(page) && @@ -1711,8 +1712,17 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, } } + /* + * We should be safe here since we are only dealing with file pages and + * we are not kswapd and therefore cannot write dirty file pages. But + * call memalloc_noreclaim_save() anyway, just in case these conditions + * change in the future. + */ + noreclaim_flag = memalloc_noreclaim_save(); nr_reclaimed = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc, &stat, true); + memalloc_noreclaim_restore(noreclaim_flag); + list_splice(&clean_pages, page_list); mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -(long)nr_reclaimed); @@ -2306,6 +2316,7 @@ unsigned long reclaim_pages(struct list_head *page_list) LIST_HEAD(node_page_list); struct reclaim_stat dummy_stat; struct page *page; + unsigned int noreclaim_flag; struct scan_control sc = { .gfp_mask = GFP_KERNEL, .priority = DEF_PRIORITY, @@ -2314,6 +2325,8 @@ unsigned long reclaim_pages(struct list_head *page_list) .may_swap = 1, }; + noreclaim_flag = memalloc_noreclaim_save(); + while (!list_empty(page_list)) { page = lru_to_page(page_list); if (nid == NUMA_NO_NODE) { @@ -2350,6 +2363,8 @@ unsigned long reclaim_pages(struct list_head *page_list) } } + memalloc_noreclaim_restore(noreclaim_flag); + return nr_reclaimed; } |