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FAILED: patch "[PATCH] mm,vmscan: Allow preallocating memory for" failed to apply to 3.18-stable tree

PATCH [email protected] 1 participant 1 message Apr 24, 2018

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Stable branch Memory management VFS MGLRU +2 more subsystems
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The patch below does not apply to the 3.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 8e04944f0ea8b838399049bdcda920ab36ae3b04 Mon Sep 17 00:00:00 2001

From: Tetsuo Handa <[email protected]>
Date: Wed, 4 Apr 2018 19:53:07 +0900
Subject: [PATCH] mm,vmscan: Allow preallocating memory for
register_shrinker().

syzbot is catching so many bugs triggered by commit 9ee332d99e4d5a97 ("sget(): handle failures of register_shrinker()"). That commit expected that calling kill_sb() from deactivate_locked_super() without successful fill_super() is safe, but the reality was different; some callers assign attributes which are needed for kill_sb() after sget() succeeds.

For example, [1] is a report where sb->s_mode (which seems to be either FMODE_READ | FMODE_EXCL | FMODE_WRITE or FMODE_READ | FMODE_EXCL) is not assigned unless sget() succeeds. But it does not worth complicate sget() so that register_shrinker() failure path can safely call kill_block_super() via kill_sb(). Making alloc_super() fail if memory allocation for register_shrinker() failed is much simpler. Let's avoid calling deactivate_locked_super() from sget_userns() by preallocating memory for the shrinker and making register_shrinker() in sget_userns() never fail.

[1] https://syzkaller.appspot.com/bug?id=588996a25a2587be2e3a54e8646728fb9cae44e7

Signed-off-by Tetsuo Handa <[email protected]>
Reported-by syzbot <[email protected]>
Cc Al Viro <[email protected]>
Cc Michal Hocko <[email protected]>
Signed-off-by Al Viro <[email protected]>
fs/super.c +4 -5
index 5fa9a8d8d865..122c402049a2 100644
@@ -167,6 +167,7 @@ static void destroy_unused_super(struct super_block *s)
 	security_sb_free(s);
 	put_user_ns(s->s_user_ns);
 	kfree(s->s_subtype);
+	free_prealloced_shrinker(&s->s_shrink);
 	/* no delays needed */
 	destroy_super_work(&s->destroy_work);
 }

@@ -252,6 +253,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_shrink.count_objects = super_cache_count;
 	s->s_shrink.batch = 1024;
 	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
+	if (prealloc_shrinker(&s->s_shrink))
+		goto fail;
 	return s;
 
 fail:

@@ -518,11 +521,7 @@ struct super_block *sget_userns(struct file_system_type *type,
 	hlist_add_head(&s->s_instances, &type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(type);
-	err = register_shrinker(&s->s_shrink);
-	if (err) {
-		deactivate_locked_super(s);
-		s = ERR_PTR(err);
-	}
+	register_shrinker_prepared(&s->s_shrink);
 	return s;
 }
include/linux/shrinker.h +5 -2
index 388ff2936a87..6794490f25b2 100644
@@ -75,6 +75,9 @@ struct shrinker {
 #define SHRINKER_NUMA_AWARE	(1 << 0)
 #define SHRINKER_MEMCG_AWARE	(1 << 1)
 
-extern int register_shrinker(struct shrinker *);
-extern void unregister_shrinker(struct shrinker *);
+extern int prealloc_shrinker(struct shrinker *shrinker);
+extern void register_shrinker_prepared(struct shrinker *shrinker);
+extern int register_shrinker(struct shrinker *shrinker);
+extern void unregister_shrinker(struct shrinker *shrinker);
+extern void free_prealloced_shrinker(struct shrinker *shrinker);
 #endif
mm/vmscan.c +20 -1
index 8b920ce3ae02..9b697323a88c 100644
@@ -303,7 +303,7 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone
 /*
  * Add a shrinker callback to be called from the vm.
  */
-int register_shrinker(struct shrinker *shrinker)
+int prealloc_shrinker(struct shrinker *shrinker)
 {
 	size_t size = sizeof(*shrinker->nr_deferred);
 

@@ -313,10 +313,29 @@ int register_shrinker(struct shrinker *shrinker)
 	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
 	if (!shrinker->nr_deferred)
 		return -ENOMEM;
+	return 0;
+}
+
+void free_prealloced_shrinker(struct shrinker *shrinker)
+{
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+}
 
+void register_shrinker_prepared(struct shrinker *shrinker)
+{
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
 	up_write(&shrinker_rwsem);
+}
+
+int register_shrinker(struct shrinker *shrinker)
+{
+	int err = prealloc_shrinker(shrinker);
+
+	if (err)
+		return err;
+	register_shrinker_prepared(shrinker);
 	return 0;
 }
 EXPORT_SYMBOL(register_shrinker);