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

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>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index c4a613688a175c4cc0e3d9c045e56a4bbb10fe79..d58361109066d67844bfbd64a41ebc33dd1bed7b 100644 (file)
--- 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);