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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2365de76e25sm57936375ad.100.2025.06.16.03.26.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jun 2025 03:26:29 -0700 (PDT) Message-ID: Date: Mon, 16 Jun 2025 19:56:23 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/5] btrfs: split btrfs_fs_devices.opened To: Johannes Thumshirn , linux-btrfs@vger.kernel.org Cc: Boris Burkov , Christoph Hellwig , David Sterba , Josef Bacik , Johannes Thumshirn References: <20250611100303.110311-1-jth@kernel.org> <20250611100303.110311-4-jth@kernel.org> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=wqu@suse.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNGFF1IFdlbnJ1byA8d3F1QHN1c2UuY29tPsLAlAQTAQgAPgIbAwULCQgHAgYVCAkKCwIE FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXVgBQkQ/lqxAAoJEMI9kfOh Jf6o+jIH/2KhFmyOw4XWAYbnnijuYqb/obGae8HhcJO2KIGcxbsinK+KQFTSZnkFxnbsQ+VY fvtWBHGt8WfHcNmfjdejmy9si2jyy8smQV2jiB60a8iqQXGmsrkuR+AM2V360oEbMF3gVvim 2VSX2IiW9KERuhifjseNV1HLk0SHw5NnXiWh1THTqtvFFY+CwnLN2GqiMaSLF6gATW05/sEd V17MdI1z4+WSk7D57FlLjp50F3ow2WJtXwG8yG8d6S40dytZpH9iFuk12Sbg7lrtQxPPOIEU rpmZLfCNJJoZj603613w/M8EiZw6MohzikTWcFc55RLYJPBWQ+9puZtx1DopW2jOwE0EWdWB rwEIAKpT62HgSzL9zwGe+WIUCMB+nOEjXAfvoUPUwk+YCEDcOdfkkM5FyBoJs8TCEuPXGXBO Cl5P5B8OYYnkHkGWutAVlUTV8KESOIm/KJIA7jJA+Ss9VhMjtePfgWexw+P8itFRSRrrwyUf E+0WcAevblUi45LjWWZgpg3A80tHP0iToOZ5MbdYk7YFBE29cDSleskfV80ZKxFv6koQocq0 vXzTfHvXNDELAuH7Ms/WJcdUzmPyBf3Oq6mKBBH8J6XZc9LjjNZwNbyvsHSrV5bgmu/THX2n g/3be+iqf6OggCiy3I1NSMJ5KtR0q2H2Nx2Vqb1fYPOID8McMV9Ll6rh8S8AEQEAAcLAfAQY AQgAJgIbDBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXWBBQkQ/lrSAAoJEMI9kfOhJf6o cakH+QHwDszsoYvmrNq36MFGgvAHRjdlrHRBa4A1V1kzd4kOUokongcrOOgHY9yfglcvZqlJ qfa4l+1oxs1BvCi29psteQTtw+memmcGruKi+YHD7793zNCMtAtYidDmQ2pWaLfqSaryjlzR /3tBWMyvIeWZKURnZbBzWRREB7iWxEbZ014B3gICqZPDRwwitHpH8Om3eZr7ygZck6bBa4MU o1XgbZcspyCGqu1xF/bMAY2iCDcq6ULKQceuKkbeQ8qxvt9hVxJC2W3lHq8dlK1pkHPDg9wO JoAXek8MF37R8gpLoGWl41FIUb3hFiu3zhDDvslYM4BmzI18QgQTQnotJH8= In-Reply-To: <20250611100303.110311-4-jth@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/6/11 19:33, Johannes Thumshirn 写道: > From: Christoph Hellwig > > The btrfs_fs_devices.opened member mixes an in use counter for the > fs_devices structure that prevents it from being garbage collected with > a flag if the underlying devices were actually opened. This not only > makes the code hard to follow, but also prevents btrfs from switching > to opening the block device only after super block creation. Split it > into an in_use counter and an is_open boolean flag instead. I'm hitting problems with this patch applied (previous patch 1 and 2 also applied and tested), that it causes problem setting up other dm devices. Thus failing future tests that requires SCRATCH_DEV for dm setup. Furthermore at btrfs unload time, the warnings at free_fs_devices() got triggered. But without this one (only patch 1 & 2), I have not hit anything like that at all. So this means, even without extra in_use without opening cases, this is already causing problems. Furthermore the in-use-but-not-opened state for the next patch (delayed devices opening), may not be that important anymore. With extra comments added into btrfs_get_tree_super(), we can explain the cleanup properly. And even if there are races between devices open (protected by uuid_mutex) and sget_fc(), and different threads win the two races, it doesn't really matter. As long as the final btrfs_fill_super() get all its devices opened, and the opened ref count is working, there is nothing to worry. So I'm afraid both patch 3 and 4 may be dropped. Thanks, Qu > > Signed-off-by: Christoph Hellwig > Signed-off-by: Johannes Thumshirn > --- > fs/btrfs/volumes.c | 53 ++++++++++++++++++++++++++-------------------- > fs/btrfs/volumes.h | 6 ++++-- > 2 files changed, 34 insertions(+), 25 deletions(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 1ebfc69012a2..00b64f98e3bd 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -413,7 +413,8 @@ static void free_fs_devices(struct btrfs_fs_devices *fs_devices) > { > struct btrfs_device *device; > > - WARN_ON(fs_devices->opened); > + WARN_ON_ONCE(fs_devices->in_use); > + WARN_ON_ONCE(fs_devices->is_open); > while (!list_empty(&fs_devices->devices)) { > device = list_first_entry(&fs_devices->devices, > struct btrfs_device, dev_list); > @@ -541,7 +542,7 @@ static int btrfs_free_stale_devices(dev_t devt, struct btrfs_device *skip_device > continue; > if (devt && devt != device->devt) > continue; > - if (fs_devices->opened) { > + if (fs_devices->in_use) { > if (devt) > ret = -EBUSY; > break; > @@ -613,7 +614,7 @@ static struct btrfs_fs_devices *find_fsid_by_device( > if (found_by_devt) { > /* Existing device. */ > if (fsid_fs_devices == NULL) { > - if (devt_fs_devices->opened == 0) { > + if (devt_fs_devices->in_use == 0) { > /* Stale device. */ > return NULL; > } else { > @@ -848,7 +849,7 @@ static noinline struct btrfs_device *device_list_add(const char *path, > if (!device) { > unsigned int nofs_flag; > > - if (fs_devices->opened) { > + if (fs_devices->in_use) { > btrfs_err(NULL, > "device %s (%d:%d) belongs to fsid %pU, and the fs is already mounted, scanned by %s (%d)", > path, MAJOR(path_devt), MINOR(path_devt), > @@ -916,7 +917,7 @@ static noinline struct btrfs_device *device_list_add(const char *path, > * tracking a problem where systems fail mount by subvolume id > * when we reject replacement on a mounted FS. > */ > - if (!fs_devices->opened && found_transid < device->generation) { > + if (!fs_devices->in_use && found_transid < device->generation) { > /* > * That is if the FS is _not_ mounted and if you > * are here, that means there is more than one > @@ -977,7 +978,7 @@ static noinline struct btrfs_device *device_list_add(const char *path, > * it back. We need it to pick the disk with largest generation > * (as above). > */ > - if (!fs_devices->opened) { > + if (!fs_devices->in_use) { > device->generation = found_transid; > fs_devices->latest_generation = max_t(u64, found_transid, > fs_devices->latest_generation); > @@ -1177,15 +1178,19 @@ static void close_fs_devices(struct btrfs_fs_devices *fs_devices) > > lockdep_assert_held(&uuid_mutex); > > - if (--fs_devices->opened > 0) > + if (--fs_devices->in_use > 0) > return; > > + if (!fs_devices->is_open) > + goto done; > + > list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list) > btrfs_close_one_device(device); > > WARN_ON(fs_devices->open_devices); > WARN_ON(fs_devices->rw_devices); > - fs_devices->opened = 0; > + fs_devices->is_open = false; > +done: > fs_devices->seeding = false; > fs_devices->fs_info = NULL; > } > @@ -1197,7 +1202,7 @@ void btrfs_close_devices(struct btrfs_fs_devices *fs_devices) > > mutex_lock(&uuid_mutex); > close_fs_devices(fs_devices); > - if (!fs_devices->opened) { > + if (!fs_devices->in_use) { > list_splice_init(&fs_devices->seed_list, &list); > > /* > @@ -1253,7 +1258,7 @@ static int open_fs_devices(struct btrfs_fs_devices *fs_devices, > return -EINVAL; > } > > - fs_devices->opened = 1; > + fs_devices->is_open = true; > fs_devices->latest_dev = latest_dev; > fs_devices->total_rw_bytes = 0; > fs_devices->chunk_alloc_policy = BTRFS_CHUNK_ALLOC_REGULAR; > @@ -1306,16 +1311,14 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices, > * We also don't need the lock here as this is called during mount and > * exclusion is provided by uuid_mutex > */ > - > - if (fs_devices->opened) { > - fs_devices->opened++; > - ret = 0; > - } else { > + if (!fs_devices->is_open) { > list_sort(NULL, &fs_devices->devices, devid_cmp); > ret = open_fs_devices(fs_devices, flags, holder); > + if (ret) > + return ret; > } > - > - return ret; > + fs_devices->in_use++; > + return 0; > } > > void btrfs_release_disk_super(struct btrfs_super_block *super) > @@ -1407,7 +1410,7 @@ static bool btrfs_skip_registration(struct btrfs_super_block *disk_super, > > mutex_lock(&fs_devices->device_list_mutex); > > - if (!fs_devices->opened) { > + if (!fs_devices->is_open) { > mutex_unlock(&fs_devices->device_list_mutex); > continue; > } > @@ -2314,13 +2317,14 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, > * This can happen if cur_devices is the private seed devices list. We > * cannot call close_fs_devices() here because it expects the uuid_mutex > * to be held, but in fact we don't need that for the private > - * seed_devices, we can simply decrement cur_devices->opened and then > + * seed_devices, we can simply decrement cur_devices->in_use and then > * remove it from our list and free the fs_devices. > */ > if (cur_devices->num_devices == 0) { > list_del_init(&cur_devices->seed_list); > - ASSERT(cur_devices->opened == 1, "opened=%d", cur_devices->opened); > - cur_devices->opened--; > + ASSERT(cur_devices->in_use == 1, "opened=%d", cur_devices->in_use); > + cur_devices->in_use--; > + cur_devices->is_open = false; > free_fs_devices(cur_devices); > } > > @@ -2549,7 +2553,8 @@ static struct btrfs_fs_devices *btrfs_init_sprout(struct btrfs_fs_info *fs_info) > list_add(&old_devices->fs_list, &fs_uuids); > > memcpy(seed_devices, fs_devices, sizeof(*seed_devices)); > - seed_devices->opened = 1; > + seed_devices->in_use = 1; > + seed_devices->is_open = true; > INIT_LIST_HEAD(&seed_devices->devices); > INIT_LIST_HEAD(&seed_devices->alloc_list); > mutex_init(&seed_devices->device_list_mutex); > @@ -7162,7 +7167,8 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info, > return fs_devices; > > fs_devices->seeding = true; > - fs_devices->opened = 1; > + fs_devices->in_use = 1; > + fs_devices->is_open = true; > return fs_devices; > } > > @@ -7179,6 +7185,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info, > free_fs_devices(fs_devices); > return ERR_PTR(ret); > } > + fs_devices->in_use = 1; > > if (!fs_devices->seeding) { > close_fs_devices(fs_devices); > diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h > index afa71d315c46..06cf8c99befe 100644 > --- a/fs/btrfs/volumes.h > +++ b/fs/btrfs/volumes.h > @@ -419,8 +419,10 @@ struct btrfs_fs_devices { > > struct list_head seed_list; > > - /* Count fs-devices opened. */ > - int opened; > + /* Count if fs_device is in used. */ > + unsigned int in_use; > + /* True if the devices were opened. */ > + bool is_open; > > /* Set when we find or add a device that doesn't have the nonrot flag set. */ > bool rotating;