| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <09210f85-8a34-1ae8-59ec-55fefe7ba81a@huaweicloud.com>
Date: Wed, 22 Nov 2023 15:06:23 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Michael Kelley <mhklinux@...look.com>,
Yu Kuai <yukuai1@...weicloud.com>,
"ming.lei@...hat.com" <ming.lei@...hat.com>,
"axboe@...nel.dk" <axboe@...nel.dk>
Cc: "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"yi.zhang@...wei.com" <yi.zhang@...wei.com>,
"yangerkun@...wei.com" <yangerkun@...wei.com>,
"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v3 2/3] block: introduce new field bd_flags in
block_device
Hi,
在 2023/11/22 11:52, Michael Kelley 写道:
> From: Yu Kuai <yukuai1@...weicloud.com> Sent: Wednesday, November 22, 2023 2:31 AM
>>
>> There are multiple switches in struct block_device, use separate bool
>> fields for them is not gracefully. Add a new field bd_flags and replace
>> swithes to a bit, there are no functional changes, and prepare to add
>> a new switch in the next patch. In order to keep bd_flags in the first
>> cacheline and prevent layout to be affected, define it as u16.
>>
>> Also add new helpers to set/clear/test each bit like 'bio->bi_flags'.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>> block/bdev.c | 15 ++++++++-------
>> block/blk-core.c | 7 ++++---
>> block/genhd.c | 15 +++++++++++----
>> block/ioctl.c | 6 +++++-
>> include/linux/blk_types.h | 27 +++++++++++++++++++++------
>> include/linux/blkdev.h | 5 +++--
>> 6 files changed, 52 insertions(+), 23 deletions(-)
>>
>> diff --git a/block/bdev.c b/block/bdev.c
>> index e4cfb7adb645..10f524a7416c 100644
>> --- a/block/bdev.c
>> +++ b/block/bdev.c
>> @@ -402,10 +402,10 @@ struct block_device *bdev_alloc(struct gendisk
>> *disk, u8 partno)
>> bdev->bd_partno = partno;
>> bdev->bd_inode = inode;
>> bdev->bd_queue = disk->queue;
>> - if (partno)
>> - bdev->bd_has_submit_bio = disk->part0->bd_has_submit_bio;
>> + if (partno && bdev_flagged(disk->part0, BD_FLAG_HAS_SUBMIT_BIO))
>> + bdev_set_flag(bdev, BD_FLAG_HAS_SUBMIT_BIO);
>> else
>> - bdev->bd_has_submit_bio = false;
>> + bdev_clear_flag(bdev, BD_FLAG_HAS_SUBMIT_BIO);
>> bdev->bd_stats = alloc_percpu(struct disk_stats);
>> if (!bdev->bd_stats) {
>> iput(inode);
>> @@ -606,7 +606,7 @@ static void bd_end_claim(struct block_device *bdev, void *holder)
>> bdev->bd_holder = NULL;
>> bdev->bd_holder_ops = NULL;
>> mutex_unlock(&bdev->bd_holder_lock);
>> - if (bdev->bd_write_holder)
>> + if (bdev_flagged(bdev, BD_FLAG_WRITE_HOLDER))
>> unblock = true;
>> }
>> if (!whole->bd_holders)
>> @@ -619,7 +619,7 @@ static void bd_end_claim(struct block_device *bdev, void *holder)
>> */
>> if (unblock) {
>> disk_unblock_events(bdev->bd_disk);
>> - bdev->bd_write_holder = false;
>> + bdev_clear_flag(bdev, BD_FLAG_WRITE_HOLDER);
>> }
>> }
>>
>> @@ -805,9 +805,10 @@ struct block_device *blkdev_get_by_dev(dev_t dev,
>> blk_mode_t mode, void *holder,
>> * writeable reference is too fragile given the way @mode is
>> * used in blkdev_get/put().
>> */
>> - if ((mode & BLK_OPEN_WRITE) && !bdev->bd_write_holder &&
>> + if ((mode & BLK_OPEN_WRITE) &&
>> + !bdev_flagged(bdev, BD_FLAG_WRITE_HOLDER) &&
>> (disk->event_flags & DISK_EVENT_FLAG_BLOCK_ON_EXCL_WRITE)) {
>> - bdev->bd_write_holder = true;
>> + bdev_set_flag(bdev, BD_FLAG_WRITE_HOLDER);
>> unblock_events = false;
>> }
>> }
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index fdf25b8d6e78..f9f8b12ba626 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -482,7 +482,8 @@ __setup("fail_make_request=",
>> setup_fail_make_request);
>>
>> bool should_fail_request(struct block_device *part, unsigned int bytes)
>> {
>> - return part->bd_make_it_fail && should_fail(&fail_make_request, bytes);
>> + return bdev_flagged(part, BD_FLAG_MAKE_IT_FAIL) &&
>> + should_fail(&fail_make_request, bytes);
>> }
>>
>> static int __init fail_make_request_debugfs(void)
>> @@ -595,7 +596,7 @@ static void __submit_bio(struct bio *bio)
>> if (unlikely(!blk_crypto_bio_prep(&bio)))
>> return;
>>
>> - if (!bio->bi_bdev->bd_has_submit_bio) {
>> + if (!bdev_flagged(bio->bi_bdev, BD_FLAG_HAS_SUBMIT_BIO)) {
>> blk_mq_submit_bio(bio);
>> } else if (likely(bio_queue_enter(bio) == 0)) {
>> struct gendisk *disk = bio->bi_bdev->bd_disk;
>> @@ -703,7 +704,7 @@ void submit_bio_noacct_nocheck(struct bio *bio)
>> */
>> if (current->bio_list)
>> bio_list_add(¤t->bio_list[0], bio);
>> - else if (!bio->bi_bdev->bd_has_submit_bio)
>> + else if (!bdev_flagged(bio->bi_bdev, BD_FLAG_HAS_SUBMIT_BIO))
>> __submit_bio_noacct_mq(bio);
>> else
>> __submit_bio_noacct(bio);
>> diff --git a/block/genhd.c b/block/genhd.c
>> index c9d06f72c587..57f96c0c8da0 100644
>> --- a/block/genhd.c
>> +++ b/block/genhd.c
>> @@ -413,7 +413,8 @@ int __must_check device_add_disk(struct device
>> *parent, struct gendisk *disk,
>> elevator_init_mq(disk->queue);
>>
>> /* Mark bdev as having a submit_bio, if needed */
>> - disk->part0->bd_has_submit_bio = disk->fops->submit_bio != NULL;
>> + if (disk->fops->submit_bio)
>> + bdev_set_flag(disk->part0, BD_FLAG_HAS_SUBMIT_BIO);
>>
>> /*
>> * If the driver provides an explicit major number it also must provide
>> @@ -1062,7 +1063,8 @@ static DEVICE_ATTR(diskseq, 0444, diskseq_show, NULL);
>> ssize_t part_fail_show(struct device *dev,
>> struct device_attribute *attr, char *buf)
>> {
>> - return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_make_it_fail);
>> + return sprintf(buf, "%d\n",
>> + bdev_flagged(dev_to_bdev(dev), BD_FLAG_MAKE_IT_FAIL));
>> }
>>
>> ssize_t part_fail_store(struct device *dev,
>> @@ -1071,8 +1073,13 @@ ssize_t part_fail_store(struct device *dev,
>> {
>> int i;
>>
>> - if (count > 0 && sscanf(buf, "%d", &i) > 0)
>> - dev_to_bdev(dev)->bd_make_it_fail = i;
>> + if (count > 0 && sscanf(buf, "%d", &i) > 0) {
>> + if (!i)
>> + bdev_clear_flag(dev_to_bdev(dev), BD_FLAG_MAKE_IT_FAIL);
>> + else
>> + bdev_set_flag(dev_to_bdev(dev), BD_FLAG_MAKE_IT_FAIL);
>> +
>> + }
>>
>> return count;
>> }
>> diff --git a/block/ioctl.c b/block/ioctl.c
>> index 4160f4e6bd5b..a64440f4c96b 100644
>> --- a/block/ioctl.c
>> +++ b/block/ioctl.c
>> @@ -394,7 +394,11 @@ static int blkdev_roset(struct block_device *bdev, unsigned cmd,
>> if (ret)
>> return ret;
>> }
>> - bdev->bd_read_only = n;
>> +
>> + if (!n)
>> + bdev_clear_flag(bdev, BD_FLAG_READ_ONLY);
>> + else
>> + bdev_set_flag(bdev, BD_FLAG_READ_ONLY);
>> return 0;
>> }
>>
>> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
>> index f7d40692dd94..de652045111b 100644
>> --- a/include/linux/blk_types.h
>> +++ b/include/linux/blk_types.h
>> @@ -37,6 +37,11 @@ struct bio_crypt_ctx;
>> #define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT)
>> #define SECTOR_MASK (PAGE_SECTORS - 1)
>>
>> +#define BD_FLAG_READ_ONLY 0 /* read-only-policy */
>> +#define BD_FLAG_WRITE_HOLDER 1
>> +#define BD_FLAG_HAS_SUBMIT_BIO 2
>> +#define BD_FLAG_MAKE_IT_FAIL 3
>> +
>> struct block_device {
>> sector_t bd_start_sect;
>> sector_t bd_nr_sectors;
>> @@ -44,10 +49,8 @@ struct block_device {
>> struct request_queue * bd_queue;
>> struct disk_stats __percpu *bd_stats;
>> unsigned long bd_stamp;
>> - bool bd_read_only; /* read-only policy */
>> + unsigned short bd_flags;
>> u8 bd_partno;
>> - bool bd_write_holder;
>> - bool bd_has_submit_bio;
>> dev_t bd_dev;
>> struct inode *bd_inode; /* will die */
>>
>> @@ -67,9 +70,6 @@ struct block_device {
>> struct super_block *bd_fsfreeze_sb;
>>
>> struct partition_meta_info *bd_meta_info;
>> -#ifdef CONFIG_FAIL_MAKE_REQUEST
>> - bool bd_make_it_fail;
>> -#endif
>> /*
>> * keep this out-of-line as it's both big and not needed in the fast
>> * path
>> @@ -86,6 +86,21 @@ struct block_device {
>> #define bdev_kobj(_bdev) \
>> (&((_bdev)->bd_device.kobj))
>>
>> +static inline bool bdev_flagged(struct block_device *bdev, unsigned int bit)
>> +{
>> + return bdev->bd_flags & (1U << bit);
>> +}
>> +
>> +static inline void bdev_set_flag(struct block_device *bdev, unsigned int bit)
>> +{
>> + bdev->bd_flags |= (1U << bit);
>> +}
>> +
>> +static inline void bdev_clear_flag(struct block_device *bdev, unsigned int bit)
>> +{
>> + bdev->bd_flags &= ~(1U << bit);
>> +}
>
> It seems like there's atomicity problem with this approach. In the above
> code, setting and clearing a bd_flag is *not* atomic with respect to
> setting/clearing some other bd_flag. For example, setting/clearing
> BD_FLAG_MAKE_IT_FAIL via the /sys interface could race with
> setting/clearing BD_FLAG_READ_ONLY via an ioctl, and one of the
> two changes could be lost. This problem wouldn't happen when
> each flag was a separate field. Admittedly, the likelihood of a
> problem with BD_FLAG_MAKE_IT_FAIL is extremely low, but
> conceptually the lack of atomicity is still wrong. There might
> be a similar problem with BD_FLAG_WRITE_HOLDER, but I
> didn't investigate thoroughly.
Thanks for the explanation, however, currently bio->bi_opf,
bio->bi_flags and req->rq_flags, and I can't understand now how do they
prevent to change bit concurrently? I'm probably missing something...
Thanks,
Kuai
>
> Michael
>
>> +
>> /*
>> * Block error status values. See block/blk-core:blk_errors for the details.
>> * Alpha cannot write a byte atomically, so we need to use 32-bit value.
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index 51fa7ffdee83..fc1d55ef5107 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -741,13 +741,14 @@ void disk_uevent(struct gendisk *disk, enum
>> kobject_action action);
>>
>> static inline int get_disk_ro(struct gendisk *disk)
>> {
>> - return disk->part0->bd_read_only ||
>> + return bdev_flagged(disk->part0, BD_FLAG_READ_ONLY) ||
>> test_bit(GD_READ_ONLY, &disk->state);
>> }
>>
>> static inline int bdev_read_only(struct block_device *bdev)
>> {
>> - return bdev->bd_read_only || get_disk_ro(bdev->bd_disk);
>> + return bdev_flagged(bdev, BD_FLAG_READ_ONLY) ||
>> + get_disk_ro(bdev->bd_disk);
>> }
>>
>> bool set_capacity_and_notify(struct gendisk *disk, sector_t size);
>> --
>> 2.39.2
>
> .
>
Powered by blists - more mailing lists