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mm/vmscan.c: fix potential deadlock in reclaim_pages()

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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>
This commit is contained in:
Yu Zhao 2021-06-30 18:49:48 -07:00 committed by Linus Torvalds
parent 4a8f021ba0
commit 2d2b8d2b67
1 changed files with 15 additions and 0 deletions
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15
mm/vmscan.c
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@ -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;
}