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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-25c37293ee5sm15988985ad.36.2025.09.11.04.12.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 04:12:16 -0700 (PDT) Message-ID: <4e254b82-b4de-4b16-a469-9c58c805938f@suse.com> Date: Thu, 11 Sep 2025 20:42:12 +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] btrfs: annotate block group access with data_race() when sorting for reclaim To: fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: <456b17e9620d5118fcca2674b365e0770b1d1fc1.1757332833.git.fdmanana@suse.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: <456b17e9620d5118fcca2674b365e0770b1d1fc1.1757332833.git.fdmanana@suse.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/9/8 21:35, fdmanana@kernel.org 写道: > From: Filipe Manana > > When sorting the block group list for reclaim we are using a block group's > used bytes counter without taking the block group's spinlock, so we can > race with a concurrent task updating it (at btrfs_update_block_group()), > which makes tools like KCSAN unhappy and report a race. > > Since the sorting is not strictly needed from a functional perspective > and such races should rarely cause any ordering changes (only load/store > tearing could cause them), not to mention that after the sorting the > ordering may no longer be accurate due to concurrent allocations and > deallocations of extents in a block group, annotate the accesses to the > used counter with data_race() to silence KCSAN and similar tools. > > Signed-off-by: Filipe Manana Reviewed-by: Qu Wenruo Thanks, Qu > --- > fs/btrfs/block-group.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c > index 239cbb01f83f..548483a84466 100644 > --- a/fs/btrfs/block-group.c > +++ b/fs/btrfs/block-group.c > @@ -1795,7 +1795,14 @@ static int reclaim_bgs_cmp(void *unused, const struct list_head *a, > bg1 = list_entry(a, struct btrfs_block_group, bg_list); > bg2 = list_entry(b, struct btrfs_block_group, bg_list); > > - return bg1->used > bg2->used; > + /* > + * Some other task may be updating the ->used field concurrently, but it > + * is not serious if we get a stale value or load/store tearing issues, > + * as sorting the list of block groups to reclaim is not critical and an > + * occasional imperfect order is ok. So silence KCSAN and avoid the > + * overhead of locking or any other synchronization. > + */ > + return data_race(bg1->used > bg2->used); > } > > static inline bool btrfs_should_reclaim(const struct btrfs_fs_info *fs_info)