[Cc Al and Dave - email thread starts http://lkml.kernel.org/r/001a113f996099503a055e793dd3@xxxxxxxxxx] On Tue 21-11-17 20:11:26, Tetsuo Handa wrote: > On 2017/11/21 16:35, syzbot wrote: > > Hello, > > > > syzkaller hit the following crash on ca91659962303d4fd5211a5e4e13df5cbb11e744 > > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master > > compiler: gcc (GCC) 7.1.1 20170620 > > .config is attached > > Raw console output is attached. > > > > Unfortunately, I don't have any reproducer for this bug yet. > > Fault injection found an unchecked register_shrinker() return code. > Wow, register_shrinker()/unregister_shinker() is possibly frequently called path? > > > struct super_block *sget_userns(struct file_system_type *type, > int (*test)(struct super_block *,void *), > int (*set)(struct super_block *,void *), > int flags, struct user_namespace *user_ns, > void *data) > { > (...snipped...) > spin_unlock(&sb_lock); > get_filesystem(type); > register_shrinker(&s->s_shrink); // Error check required. > return s; Yes, this is the case since numa aware shrinkers were introduced. I have a bit hard time to follow the code flow but why cannot we simply register the shrinker when we allocate the new super block? We still have the s_umount held so the shrinker cannot race with the registration code. Something like the totally untested and possibly wrong --- diff --git a/fs/super.c b/fs/super.c index 994db21f59bf..1eb850413fdf 100644 --- a/fs/super.c +++ b/fs/super.c @@ -506,6 +506,11 @@ struct super_block *sget_userns(struct file_system_type *type, s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns); if (!s) return ERR_PTR(-ENOMEM); + if (register_shrinker(&s->s_shrink)) { + up_write(&s->s_umount); + destroy_super(s); + return ERR_PTR(-ENOMEM); + } goto retry; } @@ -522,7 +527,6 @@ 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); - register_shrinker(&s->s_shrink); return s; } -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
