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Thu, 6 Apr 2023 07:23:58 -0400 (EDT) Message-ID: <003260d1-f1db-9d62-23fa-9acfba849782@fastmail.com> Date: Thu, 6 Apr 2023 20:23:57 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH 3/3] zonefs: convert to use kobject_is_added() Content-Language: en-US To: Greg KH Cc: Yangtao Li , xiang@kernel.org, chao@kernel.org, huyue2@coolpad.com, jefflexu@linux.alibaba.com, damien.lemoal@opensource.wdc.com, naohiro.aota@wdc.com, jth@kernel.org, rafael@kernel.org, linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20230406093056.33916-1-frank.li@vivo.com> <20230406093056.33916-3-frank.li@vivo.com> <2023040616-armory-unmade-4422@gregkh> <8ca8c138-67fd-73ed-1ce5-c090d49f31e9@fastmail.com> <2023040627-paver-recipient-3713@gregkh> <2023040627-platter-twisted-c1e6@gregkh> From: Damien Le Moal In-Reply-To: <2023040627-platter-twisted-c1e6@gregkh> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 4/6/23 20:18, Greg KH wrote: > On Thu, Apr 06, 2023 at 07:58:38PM +0900, Damien Le Moal wrote: >> On 4/6/23 19:26, Greg KH wrote: >>> On Thu, Apr 06, 2023 at 07:13:38PM +0900, Damien Le Moal wrote: >>>> On 4/6/23 19:05, Greg KH wrote: >>>>> On Thu, Apr 06, 2023 at 05:30:56PM +0800, Yangtao Li wrote: >>>>>> Use kobject_is_added() instead of local `s_sysfs_registered` variables. >>>>>> BTW kill kobject_del() directly, because kobject_put() actually covers >>>>>> kobject removal automatically. >>>>>> >>>>>> Signed-off-by: Yangtao Li >>>>>> --- >>>>>> fs/zonefs/sysfs.c | 11 +++++------ >>>>>> fs/zonefs/zonefs.h | 1 - >>>>>> 2 files changed, 5 insertions(+), 7 deletions(-) >>>>>> >>>>>> diff --git a/fs/zonefs/sysfs.c b/fs/zonefs/sysfs.c >>>>>> index 8ccb65c2b419..f0783bf7a25c 100644 >>>>>> --- a/fs/zonefs/sysfs.c >>>>>> +++ b/fs/zonefs/sysfs.c >>>>>> @@ -101,8 +101,6 @@ int zonefs_sysfs_register(struct super_block *sb) >>>>>> return ret; >>>>>> } >>>>>> >>>>>> - sbi->s_sysfs_registered = true; >>>>> >>>>> You know this, why do you need to have a variable tell you this or not? >>>> >>>> If kobject_init_and_add() fails, zonefs_sysfs_register() returns an error and >>>> fill_super will also return that error. vfs will then call kill_super, which >>>> calls zonefs_sysfs_unregister(). For that case, we need to know that we actually >>>> added the kobj. >>> >>> Ok, but then why not just 0 out the kobject pointer here instead? That >>> way you will always know if it's a valid pointer or not and you don't >>> have to rely on some other variable? Use the one that you have already :) >> >> but sbi->s_kobj is the kobject itself, not a pointer. > > Then it should not be there if the kobject is not valid as it should > have been freed when the kobject_init_and_add() call failed, right? What do you mean freed ? the kboject itself is a field of zonefs sbi. So the kobject gets freed together with sbi. >> I can still zero it out in >> case of error to avoid using the added s_sysfs_registered bool. I would need to >> check a field of s_kobj though, which is not super clean and makes the code >> dependent on kobject internals. Not super nice in my opinion, unless I am >> missing something. > > See above, if a kobject fails to be registered, just remove the whole > object as it's obviously "dead" now and you can not trust it. Well yes, that is what s_sysfs_registered indicates, that the kobject is not valid. I do not understand what you mean with "just remove the whole object". >>> And you really don't even need to check anything, just pass in NULL to >>> kobject_del() and friends, it should handle it.> >>>>>> - >>>>>> return 0; >>>>>> } >>>>>> >>>>>> @@ -110,12 +108,13 @@ void zonefs_sysfs_unregister(struct super_block *sb) >>>>>> { >>>>>> struct zonefs_sb_info *sbi = ZONEFS_SB(sb); >>>>>> >>>>>> - if (!sbi || !sbi->s_sysfs_registered) >>>>> >>>>> How can either of these ever be true? Note, sbi should be passed here >>>>> to this function, not the super block as that is now unregistered from >>>>> the system. Looks like no one has really tested this codepath that much >>>>> :( >>>>> >>>>>> + if (!sbi) >>>>>> return; >>>>> >>>>> this can not ever be true, right? >>>> >>>> Yes it can, if someone attempt to mount a non zoned device. In that case, >>>> fill_super returns early without setting sb->s_fs_info but vfs still calls >>>> kill_super. >>> >>> But you already had a sbi pointer in the place that this was called, so >>> you "know" if you need to even call into here or not. You are having to >>> look up the same pointer multiple times in this call chain, there's no >>> need for that. >> >> I am not following here. Either we check that we have sbi here in >> zonefs_sysfs_unregister(), or we conditionally call this function in >> zonefs_kill_super() with a "if (sbi)". Either way, we need to check since sbi >> can be NULL. > > In zonefs_kill_super() you have get the spi at the top of the function, > so use that, don't make zonefs_sysfs_unregister() have to compute it > again. That I can do, yes. > > But again, if the kobject fails to be registered, you have to treat the > memory contained there as not valid and get rid of it as soon as > possible. If the kobject add failed, we never touch it thanks to s_sysfs_registered. I still do not see the issue here. > > thanks, > > greg k-h