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([120.245.114.74]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a0b0a708a6sm59372525ad.97.2025.12.15.07.22.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Dec 2025 07:22:49 -0800 (PST) From: Yongpeng Yang To: Damien Le Moal , Jens Axboe , Christoph Hellwig , Ming Lei Cc: linux-block@vger.kernel.org, Yongpeng Yang , Yongpeng Yang Subject: [PATCH v4 1/2] loop: use READ_ONCE() to read lo->lo_state without locking Date: Mon, 15 Dec 2025 23:21:04 +0800 Message-ID: <20251215152104.6679-2-yangyongpeng.storage@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Yongpeng Yang When lo->lo_mutex is not held, direct access may read stale data. This patch uses READ_ONCE() to read lo->lo_state and data_race() to silence code checkers, and changes all assignments to use WRITE_ONCE(). Reviewed-by: Damien Le Moal Signed-off-by: Yongpeng Yang --- v4: - Avoid the overly long line in loop_control_get_free. v3: - Use WRITE_ONCE() instead of assignments to update lo_state. v2: - Use READ_ONCE() instead of converting lo_state to atomic_t type. --- drivers/block/loop.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 272bc608e528..32a3a5b13802 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1082,7 +1082,7 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode, /* Order wrt reading lo_state in loop_validate_file(). */ wmb(); - lo->lo_state = Lo_bound; + WRITE_ONCE(lo->lo_state, Lo_bound); if (part_shift) lo->lo_flags |= LO_FLAGS_PARTSCAN; partscan = lo->lo_flags & LO_FLAGS_PARTSCAN; @@ -1179,7 +1179,7 @@ static void __loop_clr_fd(struct loop_device *lo) if (!part_shift) set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state); mutex_lock(&lo->lo_mutex); - lo->lo_state = Lo_unbound; + WRITE_ONCE(lo->lo_state, Lo_unbound); mutex_unlock(&lo->lo_mutex); /* @@ -1218,7 +1218,7 @@ static int loop_clr_fd(struct loop_device *lo) lo->lo_flags |= LO_FLAGS_AUTOCLEAR; if (disk_openers(lo->lo_disk) == 1) - lo->lo_state = Lo_rundown; + WRITE_ONCE(lo->lo_state, Lo_rundown); loop_global_unlock(lo, true); return 0; @@ -1743,7 +1743,7 @@ static void lo_release(struct gendisk *disk) mutex_lock(&lo->lo_mutex); if (lo->lo_state == Lo_bound && (lo->lo_flags & LO_FLAGS_AUTOCLEAR)) - lo->lo_state = Lo_rundown; + WRITE_ONCE(lo->lo_state, Lo_rundown); need_clear = (lo->lo_state == Lo_rundown); mutex_unlock(&lo->lo_mutex); @@ -1858,7 +1858,7 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, blk_mq_start_request(rq); - if (lo->lo_state != Lo_bound) + if (data_race(READ_ONCE(lo->lo_state)) != Lo_bound) return BLK_STS_IOERR; switch (req_op(rq)) { @@ -2016,7 +2016,7 @@ static int loop_add(int i) lo->worker_tree = RB_ROOT; INIT_LIST_HEAD(&lo->idle_worker_list); timer_setup(&lo->timer, loop_free_idle_workers_timer, TIMER_DEFERRABLE); - lo->lo_state = Lo_unbound; + WRITE_ONCE(lo->lo_state, Lo_unbound); err = mutex_lock_killable(&loop_ctl_mutex); if (err) @@ -2174,7 +2174,7 @@ static int loop_control_remove(int idx) goto mark_visible; } /* Mark this loop device as no more bound, but not quite unbound yet */ - lo->lo_state = Lo_deleting; + WRITE_ONCE(lo->lo_state, Lo_deleting); mutex_unlock(&lo->lo_mutex); loop_remove(lo); @@ -2197,8 +2197,12 @@ static int loop_control_get_free(int idx) if (ret) return ret; idr_for_each_entry(&loop_index_idr, lo, id) { - /* Hitting a race results in creating a new loop device which is harmless. */ - if (lo->idr_visible && data_race(lo->lo_state) == Lo_unbound) + /* + * Hitting a race results in creating a new loop device + * which is harmless. + */ + if (lo->idr_visible && + data_race(READ_ONCE(lo->lo_state)) == Lo_unbound) goto found; } mutex_unlock(&loop_ctl_mutex); -- 2.43.0