idr: idr_alloc() shouldn't trigger lowmem warning when preloaded

GFP_NOIO is often used for idr_alloc() inside preloaded section as the
allocation mask doesn't really matter.  If the idr tree needs to be
expanded, idr_alloc() first tries to allocate using the specified
allocation mask and if it fails falls back to the preloaded buffer.  This
order prevent non-preloading idr_alloc() users from taking advantage of
preloading ones by using preload buffer without filling it shifting the
burden of allocation to the preload users.

Unfortunately, this allowed/expected-to-fail kmem_cache allocation ends up
generating spurious slab lowmem warning before succeeding the request from
the preload buffer.

This patch makes idr_layer_alloc() add __GFP_NOWARN to the first
kmem_cache attempt and try kmem_cache again w/o __GFP_NOWARN after
allocation from preload_buffer fails so that lowmem warning is generated
if not suppressed by the original @gfp_mask.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: David Teigland <teigland@redhat.com>
Tested-by: David Teigland <teigland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 25 insertions, 13 deletions

diff --git a/lib/idr.c b/lib/idr.c
index c6fb8295507b..322e2816f2fb 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -106,8 +106,14 @@ static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
         if (layer_idr)
                 return get_from_free_list(layer_idr);
 
-        /* try to allocate directly from kmem_cache */
-        new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
+        /*
+         * Try to allocate directly from kmem_cache.  We want to try this
+         * before preload buffer; otherwise, non-preloading idr_alloc()
+         * users will end up taking advantage of preloading ones.  As the
+         * following is allowed to fail for preloaded cases, suppress
+         * warning this time.
+         */
+        new = kmem_cache_zalloc(idr_layer_cache, gfp_mask | __GFP_NOWARN);
         if (new)
                 return new;
 
@@ -115,18 +121,24 @@ static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
          * Try to fetch one from the per-cpu preload buffer if in process
          * context.  See idr_preload() for details.
          */
-        if (in_interrupt())
-                return NULL;
-
-        preempt_disable();
-        new = __this_cpu_read(idr_preload_head);
-        if (new) {
-                __this_cpu_write(idr_preload_head, new->ary[0]);
-                __this_cpu_dec(idr_preload_cnt);
-                new->ary[0] = NULL;
+        if (!in_interrupt()) {
+                preempt_disable();
+                new = __this_cpu_read(idr_preload_head);
+                if (new) {
+                        __this_cpu_write(idr_preload_head, new->ary[0]);
+                        __this_cpu_dec(idr_preload_cnt);
+                        new->ary[0] = NULL;
+                }
+                preempt_enable();
+                if (new)
+                        return new;
         }
-        preempt_enable();
-        return new;
+
+        /*
+         * Both failed.  Try kmem_cache again w/o adding __GFP_NOWARN so
+         * that memory allocation failure warning is printed as intended.
+         */
+        return kmem_cache_zalloc(idr_layer_cache, gfp_mask);
 }
 
 static void idr_layer_rcu_free(struct rcu_head *head)