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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499740d1553sm13623455e9.7.2026.08.10.13.22.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Aug 2026 13:22:43 -0700 (PDT) From: David Carlier To: Minchan Kim , Sergey Senozhatsky Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, stable@vger.kernel.org, David Carlier Subject: [PATCH] zram: fix slot lock bit position on big-endian 64-bit Date: Mon, 10 Aug 2026 21:22:37 +0100 Message-ID: <20260810202241.2436603-1-devnexen@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Fixes: 2e8ff2f51dde ("zram: use u32 for entry ac_time tracking") Cc: stable@vger.kernel.org Signed-off-by: David Carlier --- drivers/block/zram/zram_drv.c | 6 +++--- drivers/block/zram/zram_drv.h | 14 ++++++++++++++ 2 files changed, 17 insertions(+), 3 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index d09fdca49cbd..a9b3bb1d3bef 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -74,7 +74,7 @@ static __must_check bool slot_trylock(struct zram *zram, unsigned long index) { 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 index) 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 *zram, unsigned long index) 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) diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index 4fddc582f3b8..7a55d751417e 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -15,6 +15,7 @@ #ifndef _ZRAM_DRV_H_ #define _ZRAM_DRV_H_ +#include #include #include @@ -57,6 +58,19 @@ enum zram_pageflags { __NR_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 -- 2.55.0