[PATCH] mm: fix sleeping function warning in alloc_swap_info

[Jiufei Xue <jiufei.xue@linux.alibaba.com>]

Trinity reports BUG:

sleeping function called from invalid context at mm/vmalloc.c:1477
in_atomic(): 1, irqs_disabled(): 0, pid: 12269, name: trinity-c1

[ 2748.573460] Call Trace:
[ 2748.575935]  dump_stack+0x91/0xeb
[ 2748.578512]  ___might_sleep+0x21c/0x250
[ 2748.581090]  remove_vm_area+0x1d/0x90
[ 2748.583637]  __vunmap+0x76/0x100
[ 2748.586120]  __se_sys_swapon+0xb9a/0x1220
[ 2748.598973]  do_syscall_64+0x60/0x210
[ 2748.601439]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

This is triggered by calling kvfree() inside spinlock() section in
function alloc_swap_info().
Fix this by moving the kvfree() after spin_unlock().

Fixes: 873d7bcfd066 ("mm/swapfile.c: use kvzalloc for swap_info_struct allocation")
Cc: <stable@vger.kernel.org>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
---
 mm/swapfile.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index dbac1d49469d..d26c9eac3d64 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2810,7 +2810,7 @@ late_initcall(max_swapfiles_check);
 
 static struct swap_info_struct *alloc_swap_info(void)
 {
-	struct swap_info_struct *p;
+	struct swap_info_struct *p, *tmp = NULL;
 	unsigned int type;
 	int i;
 	int size = sizeof(*p) + nr_node_ids * sizeof(struct plist_node);
@@ -2840,7 +2840,7 @@ static struct swap_info_struct *alloc_swap_info(void)
 		smp_wmb();
 		nr_swapfiles++;
 	} else {
-		kvfree(p);
+		tmp = p;
 		p = swap_info[type];
 		/*
 		 * Do not memset this entry: a racing procfs swap_next()
@@ -2853,6 +2853,8 @@ static struct swap_info_struct *alloc_swap_info(void)
 		plist_node_init(&p->avail_lists[i], 0);
 	p->flags = SWP_USED;
 	spin_unlock(&swap_lock);
+	kvfree(tmp);
+
 	spin_lock_init(&p->lock);
 	spin_lock_init(&p->cont_lock);
 
-- 
2.19.1.856.g8858448bb