mm/swapfile: Do not sleep with a spin lock held

Commit Message

Qian Cai Dec. 2, 2020, 3:15 p.m. UTC

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

Signed-off-by: Qian Cai <[e-mail]>
---
 mm/swapfile.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Andrew Morton Dec. 2, 2020, 11:15 p.m. UTC | #1

On Wed,  2 Dec 2020 10:15:49 -0500 Qian Cai <[e-mail]> wrote:

> We can't call kvfree() with a spin lock held, so defer it.
> 

Fixes: 873d7bcfd066 ("mm/swapfile.c: use kvzalloc for swap_info_struct allocatio
n")

Do you think it's worth a cc:stable?  IOW, is this known to ever
produce a warning?

(If not, why did we need 873d7bcfd066??)

Qian Cai Dec. 2, 2020, 11:39 p.m. UTC | #2

On Wed, 2020-12-02 at 15:15 -0800, Andrew Morton wrote:
> On Wed,  2 Dec 2020 10:15:49 -0500 Qian Cai <[e-mail]> wrote:
> 
> > We can't call kvfree() with a spin lock held, so defer it.
> > 
> 
> Fixes: 873d7bcfd066 ("mm/swapfile.c: use kvzalloc for swap_info_struct
> allocatio
> n")
> 
> Do you think it's worth a cc:stable?  IOW, is this known to ever
> produce a warning?

Yes, it did trigger a might_sleep() warning.

Patch

diff --git a/mm/swapfile.c b/mm/swapfile.c
index c4a613688a17..d58361109066 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2867,6 +2867,7 @@  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;
 
@@ -2895,7 +2896,7 @@  static struct swap_info_struct *alloc_swap_info(void)
 		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()
@@ -2908,6 +2909,7 @@  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(defer);
 	spin_lock_init(&p->lock);
 	spin_lock_init(&p->cont_lock);