The patch titled
Subject: mm/vmscan.c: fix potential deadlock in reclaim_pages()
has been removed from the -mm tree. Its filename was
mm-vmscanc-fix-potential-deadlock-in-reclaim_pages.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Yu Zhao <yuzhao@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20210614194727.2684053-1-yuzhao@xxxxxxxxxx
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
--- a/mm/vmscan.c~mm-vmscanc-fix-potential-deadlock-in-reclaim_pages
+++ a/mm/vmscan.c
@@ -1701,6 +1701,7 @@ unsigned int reclaim_clean_pages_from_li
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_li
}
}
+ /*
+ * 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_
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_
.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_
}
}
+ memalloc_noreclaim_restore(noreclaim_flag);
+
return nr_reclaimed;
}
_
Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are
