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Fri, 14 Aug 2026 15:13:26 -0700 (PDT) Message-ID: <7845cec2-adf1-408f-b7eb-019a5cd398f7@suse.com> Date: Sat, 15 Aug 2026 07:43:21 +0930 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] btrfs: free qgroup configuration when quota enable fails To: Guanjie Chen Cc: clm@fb.com, dsterba@suse.com, fdmanana@suse.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org References: <694e88fd-a165-4518-88d4-cb2f22e8925b@suse.com> <20260814123034.19289-1-jk.chen1095@gmail.com> 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: <20260814123034.19289-1-jk.chen1095@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/8/14 22:00, Guanjie Chen 写道: > Hi Qu, > >> We can reach this out branch if btrfs_start_transaction() failed, but >> the fs_info->quota_root is already setup by another process. > > Do you mean the window where qgroup_ioctl_lock is dropped before > btrfs_start_transaction()? > > I don't think another task can set fs_info->quota_root in that window. > The quota ioctl holds fs_info->subvol_sem for writing across the whole > btrfs_quota_enable() call, including while qgroup_ioctl_lock is dropped. > > As far as I can see, quota_root is only set in two places: > btrfs_quota_enable(), which is serialized by subvol_sem, and > btrfs_read_roots(), which runs during mount initialization. Right, I missed that rwsem. But still, for error handling one should be in the reverse order. And for out: label, there are cases we're going out label without creating any qgroup. In that case, qgroups removing should be done only for cases where a qgroup is created. > > The disable path also calls btrfs_free_qgroup_config() and relies on the > same subvol_sem and qgroup_ioctl_lock serialization for the qgroup > configuration. If subvol_sem did not prevent another quota operation > here, the disable path would have a similar lifetime problem. > > So if quota_root was NULL at the first check, I believe it must still be > NULL when btrfs_start_transaction() fails. I agree that the changelog > should have mentioned subvol_sem as part of the protection. > > Did I miss another runtime path that can set quota_root without holding > subvol_sem? > > Also, just to clarify, this is not my first btrfs contribution, although > my previous change was only a small one. The same, LLM disclosure if you're using it. Nowadays I won't trust anyone who is not a regular contributor. > > Thanks, > Guanjie