* [PATCH] mm/vmscan.c: fix potential deadlock in reclaim_pages()
@ 2021-06-14 19:47 Yu Zhao
2021-06-14 22:10 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Yu Zhao @ 2021-06-14 19:47 UTC (permalink / raw)
To: Andrew Morton, Minchan Kim; +Cc: linux-mm, Yu Zhao
Use memalloc_noreclaim_save()/memalloc_noreclaim_restore() in
reclaim_pages() to prevent the page reclaim from going into the block
I/O layer recursively and deadlock.
Signed-off-by: Yu Zhao <yuzhao@google.com>
---
mm/vmscan.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5199b9696bab..2a02739b20f4 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;
}
--
2.32.0.272.g935e593368-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/vmscan.c: fix potential deadlock in reclaim_pages()
2021-06-14 19:47 [PATCH] mm/vmscan.c: fix potential deadlock in reclaim_pages() Yu Zhao
@ 2021-06-14 22:10 ` Andrew Morton
2021-06-22 7:46 ` [PATCH v2] " Yu Zhao
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2021-06-14 22:10 UTC (permalink / raw)
To: Yu Zhao; +Cc: Minchan Kim, linux-mm
On Mon, 14 Jun 2021 13:47:27 -0600 Yu Zhao <yuzhao@google.com> wrote:
> Use memalloc_noreclaim_save()/memalloc_noreclaim_restore() in
> reclaim_pages() to prevent the page reclaim from going into the block
> I/O layer recursively and deadlock.
Well. Deadlocking the kernel is considered a bad thing ;)
From the lack of a cc:stable I'm assuming that this is a theoretical
from-code-inspection thing and that such a deadlock has not been
observed?
If not, why do we think that is the case? What is saving us?
(In other words, more detailed changelogging, please!)
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH v2] mm/vmscan.c: fix potential deadlock in reclaim_pages()
2021-06-14 22:10 ` Andrew Morton
@ 2021-06-22 7:46 ` Yu Zhao
0 siblings, 0 replies; 3+ messages in thread
From: Yu Zhao @ 2021-06-22 7:46 UTC (permalink / raw)
To: Andrew Morton, Minchan Kim; +Cc: linux-mm, Yu Zhao
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.
Signed-off-by: Yu Zhao <yuzhao@google.com>
---
v1 -> v2: update the commit message pre request
mm/vmscan.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5199b9696bab..2a02739b20f4 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;
}
--
2.32.0.288.g62a8d224e6-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2021-06-14 19:47 [PATCH] mm/vmscan.c: fix potential deadlock in reclaim_pages() Yu Zhao
2021-06-14 22:10 ` Andrew Morton
2021-06-22 7:46 ` [PATCH v2] " Yu Zhao
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