[merged mm-stable] zram-fix-slot-lock-bit-position-on-big-endian-64-bit.patch removed from -mm tree

The quilt patch titled
     Subject: zram: fix slot lock bit position on big-endian 64-bit
has been removed from the -mm tree.  Its filename was
     zram-fix-slot-lock-bit-position-on-big-endian-64-bit.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: David Carlier <[email protected]>
Subject: zram: fix slot lock bit position on big-endian 64-bit
Date: Mon, 10 Aug 2026 21:22:37 +0100

The slot lock is a bit operation on the whole __lock word, which flags and
ac_time alias as two u32s.  On little-endian the lock bit lands in the
position ZRAM_ENTRY_LOCK reserves in flags, so the aliasing works out.  On
64-bit big-endian it lands in ac_time instead: with
ZRAM_TRACK_ENTRY_ACTIME enabled, storing the access time from
mark_slot_accessed() or slot_free() wipes out the held lock bit, letting
another CPU take the same slot lock; an access time value with that bit
set makes the slot look locked forever.

Shift the lock bit into the flags half of the word on big-endian 64-bit.

Link: https://lore.kernel.org/[email protected]
Fixes: 2e8ff2f51dde ("zram: use u32 for entry ac_time tracking")
Signed-off-by: David Carlier <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 drivers/block/zram/zram_drv.c |    6 +++---
 drivers/block/zram/zram_drv.h |   14 ++++++++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)

--- a/drivers/block/zram/zram_drv.c~zram-fix-slot-lock-bit-position-on-big-endian-64-bit
+++ a/drivers/block/zram/zram_drv.c
@@ -74,7 +74,7 @@ static __must_check bool slot_trylock(st
 {
 	unsigned long *lock = &zram->table[index].__lock;
 
-	if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) {
+	if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK_BIT, lock)) {
 		mutex_acquire(&zram->table_lock_map, 0, 1, _RET_IP_);
 		lock_acquired(&zram->table_lock_map, _RET_IP_);
 		return true;
@@ -88,7 +88,7 @@ static void slot_lock(struct zram *zram,
 	unsigned long *lock = &zram->table[index].__lock;
 
 	mutex_acquire(&zram->table_lock_map, 0, 0, _RET_IP_);
-	wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE);
+	wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK_BIT, TASK_UNINTERRUPTIBLE);
 	lock_acquired(&zram->table_lock_map, _RET_IP_);
 }
 
@@ -97,7 +97,7 @@ static void slot_unlock(struct zram *zra
 	unsigned long *lock = &zram->table[index].__lock;
 
 	mutex_release(&zram->table_lock_map, _RET_IP_);
-	clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock);
+	clear_and_wake_up_bit(ZRAM_ENTRY_LOCK_BIT, lock);
 }
 
 static inline bool init_done(struct zram *zram)
--- a/drivers/block/zram/zram_drv.h~zram-fix-slot-lock-bit-position-on-big-endian-64-bit
+++ a/drivers/block/zram/zram_drv.h
@@ -15,6 +15,7 @@
 #ifndef _ZRAM_DRV_H_
 #define _ZRAM_DRV_H_
 
+#include <asm/byteorder.h>
 #include <linux/rwsem.h>
 #include <linux/zsmalloc.h>
 
@@ -58,6 +59,19 @@ enum zram_pageflags {
 };
 
 /*
+ * The slot lock is a bit-wait lock on the whole __lock word, while
+ * flags and ac_time alias that word as two u32s.  The lock bit must
+ * land in the slot that ZRAM_ENTRY_LOCK reserves in attr.flags; on
+ * 64-bit big-endian the flags word maps to the upper half of __lock,
+ * so the bit position has to be shifted up.
+ */
+#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
+#define ZRAM_ENTRY_LOCK_BIT  (ZRAM_ENTRY_LOCK + 32)
+#else
+#define ZRAM_ENTRY_LOCK_BIT  ZRAM_ENTRY_LOCK
+#endif
+
+/*
  * Allocated for each disk page.  We use bit-lock (ZRAM_ENTRY_LOCK bit
  * of flags) to save memory.  There can be plenty of entries and standard
  * locking primitives (e.g. mutex) will significantly increase sizeof()
_

Patches currently in -mm which might be from [email protected] are

mm-swap-pm-hibernate-atomically-replace-hibernation-pin.patch