Merge tag 'locking-urgent-2020-03-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull futex fix from Thomas Gleixner:
 "Fix for yet another subtle futex issue.

  The futex code used ihold() to prevent inodes from vanishing, but
  ihold() does not guarantee inode persistence. Replace the inode
  pointer with a per boot, machine wide, unique inode identifier.

  The second commit fixes the breakage of the hash mechanism which
  causes a 100% performance regression"

* tag 'locking-urgent-2020-03-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Unbreak futex hashing
  futex: Fix inode life-time issue

2 files changed, 11 insertions, 7 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3cd4fe6b845e..abedbffe2c9e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -698,6 +698,7 @@ struct inode {
 		struct rcu_head		i_rcu;
 	};
 	atomic64_t		i_version;
+	atomic64_t		i_sequence; /* see futex */
 	atomic_t		i_count;
 	atomic_t		i_dio_count;
 	atomic_t		i_writecount;
diff --git a/include/linux/futex.h b/include/linux/futex.h
index 5cc3fed27d4c..b70df27d7e85 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -31,23 +31,26 @@ struct task_struct;
 
 union futex_key {
 	struct {
+		u64 i_seq;
 		unsigned long pgoff;
-		struct inode *inode;
-		int offset;
+		unsigned int offset;
 	} shared;
 	struct {
+		union {
+			struct mm_struct *mm;
+			u64 __tmp;
+		};
 		unsigned long address;
-		struct mm_struct *mm;
-		int offset;
+		unsigned int offset;
 	} private;
 	struct {
+		u64 ptr;
 		unsigned long word;
-		void *ptr;
-		int offset;
+		unsigned int offset;
 	} both;
 };
 
-#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = NULL } }
+#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = 0ULL } }
 
 #ifdef CONFIG_FUTEX
 enum {