From patchwork Sun Sep 8 00:07:04 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Damien Le Moal X-Patchwork-Id: 13795296 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A52B010F4 for ; Sun, 8 Sep 2024 00:07:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725754027; cv=none; b=CsjpJuezUekUYJpwdPwY0yJ/4PQNznPuOQT/D9A0aMGCUUviiUpfXm+BGR1Jf/SRNjwSH9N1IvWoejiQm8Uldd7WDLLVdpg6IZizSmoPqF2752L6jLfbf4e2Ef/5AXMJd9DgXgDT8U7g97UDdmGwL3nPZbLbaXi2uun+0SXSUBQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725754027; c=relaxed/simple; bh=WeLm/v2C4ziwvqBeuTEjjpNp6w4mY0o4Qoc0HRLL5Ug=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=TMW+4nvOVVTgR/9GfTmOr8qKBSXjXyyYeUd1geU5xOp8zjhK1F0XHBIfZ+Yxib5PkyrkvyUI7J9Lmeoxur+9aBxlejTDqHKp6EJfFhPEicL8qj7b8AuERxdT9Jd4u7gSPwlhXtcPfKcb7zQw79KWQgZUILp47NMcLp52kaUygvM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=o2Uq0KZw; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="o2Uq0KZw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA68FC4CEC2; Sun, 8 Sep 2024 00:07:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725754027; bh=WeLm/v2C4ziwvqBeuTEjjpNp6w4mY0o4Qoc0HRLL5Ug=; h=From:To:Cc:Subject:Date:From; b=o2Uq0KZwcn/T+HkJIif0aqD0W603sbNN976viXn+sWIlsEAOvsY+MMQOkfhEtFYXQ cu17S+PLdFPIIA8IiGR/RWBIMMIJel/DetBDVqvuV9aqqpUU29JIiGfdHIeFZXa1I/ BF41V8R1fGCMfo/HzYhrJcfsERWXHr/CXOMRhGg8PbHW6Cn76B2lEuakKnhCwU09I+ 1wNxjMZBJ5XDoHXOGYgoeVWd9xee1YX8b4y0LfWpMaDw9nLgMYJnGancuqLYTpyvTz /T6ts4xCzlGUJPdbPd0D4WqRkXG4XknXbT77JF6RYRZ3SwpsiFNHTMNpMO3xFXmsVK 2LsuqdNWLQ3gA== From: Damien Le Moal To: Jens Axboe , linux-block@vger.kernel.org Cc: "Richard W . M . Jones" , Ming Lei , Jeff Moyer , Jiri Jaburek , Christoph Hellwig , Bart Van Assche , Hannes Reinecke , Chaitanya Kulkarni Subject: [PATCH] block: Prevent deadlocks when switching elevators Date: Sun, 8 Sep 2024 09:07:04 +0900 Message-ID: <20240908000704.414538-1-dlemoal@kernel.org> X-Mailer: git-send-email 2.46.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Commit af2814149883 ("block: freeze the queue in queue_attr_store") changed queue_attr_store() to always freeze a sysfs attribute queue before calling the attribute store() method, to ensure that no IOs are in-flight when an attribute value is being updated. However, this change created a potential deadlock situation for the scheduler queue attribute as changing the queue elevator with elv_iosched_store() can result in a call to request_module() if the user requested module is not already registered. If the file of the requested module is stored on the block device of the frozen queue, a deadlock will happen as the read operations triggered by request_module() will wait for the queue freeze to end. Solve this issue by introducing the load_module method in struct queue_sysfs_entry, and to calling this method function in queue_attr_store() before freezing the attribute queue. The macro definition QUEUE_RW_LOAD_MODULE_ENTRY() is added to define a queue sysfs attribute that needs loading a module. The definition of the scheduler atrribute is changed to using QUEUE_RW_LOAD_MODULE_ENTRY(), with the function elv_iosched_load_module() defined as the load_module method. elv_iosched_store() can then be simplified to remove the call to request_module(). Reported-by: Richard W.M. Jones Reported-by: Jiri Jaburek Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166 Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") Cc: stable@vger.kernel.org Signed-off-by: Damien Le Moal Tested-by: Richard W.M. Jones --- block/blk-sysfs.c | 22 +++++++++++++++++++++- block/elevator.c | 21 +++++++++++++++------ block/elevator.h | 2 ++ 3 files changed, 38 insertions(+), 7 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 60116d13cb80..e85941bec857 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -23,6 +23,7 @@ struct queue_sysfs_entry { struct attribute attr; ssize_t (*show)(struct gendisk *disk, char *page); + int (*load_module)(struct gendisk *disk, const char *page, size_t count); ssize_t (*store)(struct gendisk *disk, const char *page, size_t count); }; @@ -413,6 +414,14 @@ static struct queue_sysfs_entry _prefix##_entry = { \ .store = _prefix##_store, \ }; +#define QUEUE_RW_LOAD_MODULE_ENTRY(_prefix, _name) \ +static struct queue_sysfs_entry _prefix##_entry = { \ + .attr = { .name = _name, .mode = 0644 }, \ + .show = _prefix##_show, \ + .load_module = _prefix##_load_module, \ + .store = _prefix##_store, \ +} + QUEUE_RW_ENTRY(queue_requests, "nr_requests"); QUEUE_RW_ENTRY(queue_ra, "read_ahead_kb"); QUEUE_RW_ENTRY(queue_max_sectors, "max_sectors_kb"); @@ -420,7 +429,7 @@ QUEUE_RO_ENTRY(queue_max_hw_sectors, "max_hw_sectors_kb"); QUEUE_RO_ENTRY(queue_max_segments, "max_segments"); QUEUE_RO_ENTRY(queue_max_integrity_segments, "max_integrity_segments"); QUEUE_RO_ENTRY(queue_max_segment_size, "max_segment_size"); -QUEUE_RW_ENTRY(elv_iosched, "scheduler"); +QUEUE_RW_LOAD_MODULE_ENTRY(elv_iosched, "scheduler"); QUEUE_RO_ENTRY(queue_logical_block_size, "logical_block_size"); QUEUE_RO_ENTRY(queue_physical_block_size, "physical_block_size"); @@ -670,6 +679,17 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr, if (!entry->store) return -EIO; + /* + * If the attribute needs to load a module, do it before freezing the + * queue to ensure that the module file can be read when the request + * queue is the one for the device storing the module file. + */ + if (entry->load_module) { + res = entry->load_module(disk, page, length); + if (res) + return res; + } + blk_mq_freeze_queue(q); mutex_lock(&q->sysfs_lock); res = entry->store(disk, page, length); diff --git a/block/elevator.c b/block/elevator.c index f13d552a32c8..c355b55d0107 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -698,17 +698,26 @@ static int elevator_change(struct request_queue *q, const char *elevator_name) return 0; e = elevator_find_get(q, elevator_name); - if (!e) { - request_module("%s-iosched", elevator_name); - e = elevator_find_get(q, elevator_name); - if (!e) - return -EINVAL; - } + if (!e) + return -EINVAL; ret = elevator_switch(q, e); elevator_put(e); return ret; } +int elv_iosched_load_module(struct gendisk *disk, const char *buf, + size_t count) +{ + char elevator_name[ELV_NAME_MAX]; + + if (!elv_support_iosched(disk->queue)) + return -EOPNOTSUPP; + + strscpy(elevator_name, buf, sizeof(elevator_name)); + + return request_module("%s-iosched", strstrip(elevator_name)); +} + ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, size_t count) { diff --git a/block/elevator.h b/block/elevator.h index 3fe18e1a8692..2a78544bf201 100644 --- a/block/elevator.h +++ b/block/elevator.h @@ -148,6 +148,8 @@ extern void elv_unregister(struct elevator_type *); * io scheduler sysfs switching */ ssize_t elv_iosched_show(struct gendisk *disk, char *page); +int elv_iosched_load_module(struct gendisk *disk, const char *page, + size_t count); ssize_t elv_iosched_store(struct gendisk *disk, const char *page, size_t count); extern bool elv_bio_merge_ok(struct request *, struct bio *);