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Mon, 05 Oct 2026 14:40:01 -0700 (PDT) Message-ID: <4dcfce5e-032b-4f18-b4f1-bde5e29e2292@suse.com> Date: Tue, 6 Oct 2026 08:09:56 +1030 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: preserve caller ownership of anon_dev on root insert retry To: sungbyeongchan , David Sterba , Chris Mason Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261005212355.428030-1-tjdqudcks0424@naver.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 FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJqqw0NBQkUl/JeAAoJEMI9kfOh Jf6o/xYH/3AaWnGSq58XnY/T3/YYjr6g+TUZxa7MPyiYTELNpNlvmNlbtbAL0nW0LNvkeiqf SmYA+xkwY4RbxnZYQK0H5iv2w1eqa9qqFZb4bIBRmTapu26GEEkpad0W0ZhoSPMO8bV2Bwkf YdtPZQLaeUKvHZqNqBKnmtRLQj2Cgy3kuXX3bEGvWjzUOxPUSCj/S++JWBewMdMBPT62vZM0 3156gfn5mHA94s2p+NFJoWkERY+JPTMu9NISkpD7yuGhXN88qd/aqD0RrlhxvKsrQogdPwn9 vP18FGG3CRlHtOvOLVoY5NKSOWTDc+o+8t2XEETFTGbKYTcqeTzi4SxhvBLtTinOwE0EWdWB 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: <20261005212355.428030-1-tjdqudcks0424@naver.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/10/6 07:53, sungbyeongchan 写道: > create_subvol() preallocates an anonymous block-device ID and passes it to > btrfs_get_new_fs_root(). On a cache miss, btrfs_get_root_ref() assigns that ID > to a temporary root before attempting to insert the root in the cache. > > If another caller inserts the same root first, the creator gets -EEXIST and > drops the temporary root. The final put frees root->anon_dev, but the caller's > *anon_dev still contains the same ID. The retry finds the cached root and > frees the caller's ID again, producing an ida_free warning. Please provide the warning message. > > Keep ownership with the caller across the retry by clearing the losing > temporary root's anon_dev when the ID was supplied by the caller. Roots that > allocated their own ID retain the existing destruction behavior. > > The unfixed sequence was reproduced in two clean boots. And reproducer. > With this change the > creator-side -EEXIST branch was exercised twice, each caller-owned ID was > released exactly once on retry, no ida_free warning occurred, and ordinary > subvolume creation, writes, qgroup display, and clean unmount passed. > > Fixes: 2dfb1e43f57d ("btrfs: preallocate anon block device at first phase of snapshot creation") > Reported-by: sungbyeongchan > Tested-by: sungbyeongchan > Assisted-by: LLM > Signed-off-by: sungbyeongchan > Cc: stable@vger.kernel.org > --- > fs/btrfs/disk-io.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index dc7ad92876c0..4a5e43dfde6f 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -1355,6 +1355,8 @@ again: > ret = btrfs_insert_fs_root(fs_info, root); > if (ret) { > if (ret == -EEXIST) { > + if (anon_dev && *anon_dev) > + root->anon_dev = 0; > btrfs_put_root(root); > goto again; > }