[PATCH 4.19 23/39] mm/swapfile: do not sleep with a spin lock held

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Qian Cai <qcai@redhat.com>

commit b11a76b37a5aa7b07c3e3eeeaae20b25475bddd3 upstream.

We can't call kvfree() with a spin lock held, so defer it.  Fixes a
might_sleep() runtime warning.

Fixes: 873d7bcfd066 ("mm/swapfile.c: use kvzalloc for swap_info_struct allocation")
Signed-off-by: Qian Cai <qcai@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201202151549.10350-1-qcai@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/swapfile.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2825,6 +2825,7 @@ late_initcall(max_swapfiles_check);
 static struct swap_info_struct *alloc_swap_info(void)
 {
 	struct swap_info_struct *p;
+	struct swap_info_struct *defer = NULL;
 	unsigned int type;
 	int i;
 	int size = sizeof(*p) + nr_node_ids * sizeof(struct plist_node);
@@ -2854,7 +2855,7 @@ static struct swap_info_struct *alloc_sw
 		smp_wmb();
 		WRITE_ONCE(nr_swapfiles, nr_swapfiles + 1);
 	} else {
-		kvfree(p);
+		defer = p;
 		p = swap_info[type];
 		/*
 		 * Do not memset this entry: a racing procfs swap_next()
@@ -2867,6 +2868,7 @@ static struct swap_info_struct *alloc_sw
 		plist_node_init(&p->avail_lists[i], 0);
 	p->flags = SWP_USED;
 	spin_unlock(&swap_lock);
+	kvfree(defer);
 	spin_lock_init(&p->lock);
 	spin_lock_init(&p->cont_lock);