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Wed, 27 Aug 2025 16:35:56 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=harmstone.com; s=mail; t=1756308956; bh=DaEgoipmK3t0lfyGiGHvch7WYqM3DiVYXdh1XFZaVAE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jB1zSPVhfBJbvdXOhX2nhop6Fr3/vMAlrnlAHBOjxGKhBvRV8ybwBxxUHvuHsac5/ RMkbT06mxCq5/bvelHTIzsqPFhIWUjTQ/uv6sL4Lzdw0uUh/r8T05Mp15VtIERyY2V qJlaAEj9vTNgKNImwnmFX23fsDrmKblKwCGp12SI= Message-ID: Date: Wed, 27 Aug 2025 16:35:56 +0100 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Subject: Re: [PATCH v2 09/16] btrfs: release BG lock before calling btrfs_link_bg_list() To: Boris Burkov Cc: linux-btrfs@vger.kernel.org References: <20250813143509.31073-1-mark@harmstone.com> <20250813143509.31073-10-mark@harmstone.com> <20250816003233.GF3042054@zen.localdomain> Content-Language: en-US From: Mark Harmstone Autocrypt: addr=mark@harmstone.com; keydata= xsBNBFp/GMsBCACtFsuHZqHWpHtHuFkNZhMpiZMChyou4X8Ueur3XyF8KM2j6TKkZ5M/72qT EycEM0iU1TYVN/Rb39gBGtRclLFVY1bx4i+aUCzh/4naRxqHgzM2SeeLWHD0qva0gIwjvoRs FP333bWrFKPh5xUmmSXBtBCVqrW+LYX4404tDKUf5wUQ9bQd2ItFRM2mU/l6TUHVY2iMql6I s94Bz5/Zh4BVvs64CbgdyYyQuI4r2tk/Z9Z8M4IjEzQsjSOfArEmb4nj27R3GOauZTO2aKlM 8821rvBjcsMk6iE/NV4SPsfCZ1jvL2UC3CnWYshsGGnfd8m2v0aLFSHZlNd+vedQOTgnABEB AAHNI01hcmsgSGFybXN0b25lIDxtYXJrQGhhcm1zdG9uZS5jb20+wsCRBBMBCAA7AhsvBQsJ CAcCBhUICQoLAgQWAgMBAh4BAheAFiEEG2JgKYgV0WRwIJAqbKyhHeAWK+0FAmRQOkICGQEA CgkQbKyhHeAWK+22wgf/dBOJ0pHdkDi5fNmWynlxteBsy3VCo0qC25DQzGItL1vEY95EV4uX re3+6eVRBy9gCKHBdFWk/rtLWKceWVZ86XfTMHgy+ZnIUkrD3XZa3oIV6+bzHgQ15rXXckiE A5N+6JeY/7hAQpSh/nOqqkNMmRkHAZ1ZA/8KzQITe1AEULOn+DphERBFD5S/EURvC8jJ5hEr lQj8Tt5BvA57sLNBmQCE19+IGFmq36EWRCRJuH0RU05p/MXPTZB78UN/oGT69UAIJAEzUzVe sN3jiXuUWBDvZz701dubdq3dEdwyrCiP+dmlvQcxVQqbGnqrVARsGCyhueRLnN7SCY1s5OHK ls7ATQRafxjLAQgAvkcSlqYuzsqLwPzuzoMzIiAwfvEW3AnZxmZn9bQ+ashB9WnkAy2FZCiI /BPwiiUjqgloaVS2dIrVFAYbynqSbjqhki+uwMliz7/jEporTDmxx7VGzdbcKSCe6rkE/72o 6t7KG0r55cmWnkdOWQ965aRnRAFY7Zzd+WLqlzeoseYsNj36RMaqNR7aL7x+kDWnwbw+jgiX tgNBcnKtqmJc04z/sQTa+sUX53syht1Iv4wkATN1W+ZvQySxHNXK1r4NkcDA9ZyFA3NeeIE6 ejiO7RyC0llKXk78t0VQPdGS6HspVhYGJJt21c5vwSzIeZaneKULaxXGwzgYFTroHD9n+QAR AQABwsGsBBgBCAAgFiEEG2JgKYgV0WRwIJAqbKyhHeAWK+0FAlp/GMsCGy4BQAkQbKyhHeAW K+3AdCAEGQEIAB0WIQR6bEAu0hwk2Q9ibSlt5UHXRQtUiwUCWn8YywAKCRBt5UHXRQtUiwdE B/9OpyjmrshY40kwpmPwUfode2Azufd3QRdthnNPAY8Tv9erwsMS3sMh+M9EP+iYJh+AIRO7 fDN/u0AWIqZhHFzCndqZp8JRYULnspXSKPmVSVRIagylKew406XcAVFpEjloUtDhziBN7ykk srAMoLASaBHZpAfp8UAGDrr8Fx1on46rDxsWbh1K1h4LEmkkVooDELjsbN9jvxr8ym8Bkt54 FcpypTOd8jkt/lJRvnKXoL3rZ83HFiUFtp/ZkveZKi53ANUaqy5/U5v0Q0Ppz9ujcRA9I/V3 B66DKMg1UjiigJG6espeIPjXjw0n9BCa9jqGICyJTIZhnbEs1yEpsM87eUIH/0UFLv0b8IZe pL/3QfiFoYSqMEAwCVDFkCt4uUVFZczKTDXTFkwm7zflvRHdy5QyVFDWMyGnTN+Bq48Gwn1M uRT/Sg37LIjAUmKRJPDkVr/DQDbyL6rTvNbA3hTBu392v0CXFsvpgRNYaT8oz7DDBUUWj2Ny 6bZCBtwr/O+CwVVqWRzKDQgVo4t1xk2ts1F0R1uHHLsX7mIgfXBYdo/y4UgFBAJH5NYUcBR+ QQcOgUUZeF2MC9i0oUaHJOIuuN2q+m9eMpnJdxVKAUQcZxDDvNjZwZh+ejsgG4Ejd2XR/T0y XFoR/dLFIhf2zxRylN1xq27M9P2t1xfQFocuYToPsVk= In-Reply-To: <20250816003233.GF3042054@zen.localdomain> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16/08/2025 1.32 am, Boris Burkov wrote: > On Wed, Aug 13, 2025 at 03:34:51PM +0100, Mark Harmstone wrote: >> Release block_group->lock before calling btrfs_link_bg_list() in >> btrfs_delete_unused_bgs(), as this was causing lockdep issues. >> >> This lock isn't held in any other place that we call btrfs_link_bg_list(), as >> the block group lists are manipulated while holding fs_info->unused_bgs_lock. >> > > Please include the offending lockdep output you are fixing. I didn't include it as lockdep was triggering on the second (correct) instance, while the problem was on the first (incorrect) instance, and thought it would confuse matters. And I stupidly didn't take a copy, and now I can't reproduce it. The issue is that in btrfs_discard_punt_unused_bgs_list() in "btrfs: remove remapped block groups from the free-space tree", we're holding unused_bgs_lock then looping through the list grabbing the individual block group list. In btrfs_delete_unused_bgs() we're grabbing unused_bgs_lock while unnecessarily holding the block group lock. > Is this a generic fix unrelated to your other changes? I think a > separate patch from the series is clearer in that case. And it would > need a Fixes: tag (probably my patch that added btrfs_link_bg_list, haha) It looks like it's actually f4a9f219411f318ae60d6ff7f129082a75686c6c, "btrfs: do not delete unused block group if it may be used soon". > > Thanks. > >> Signed-off-by: Mark Harmstone >> --- >> fs/btrfs/block-group.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c >> index bed9c58b6cbc..8c28f829547e 100644 >> --- a/fs/btrfs/block-group.c >> +++ b/fs/btrfs/block-group.c >> @@ -1620,6 +1620,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info) >> if ((space_info->total_bytes - block_group->length < used && >> block_group->zone_unusable < block_group->length) || >> has_unwritten_metadata(block_group)) { >> + spin_unlock(&block_group->lock); >> + >> /* >> * Add a reference for the list, compensate for the ref >> * drop under the "next" label for the >> @@ -1628,7 +1630,6 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info) >> btrfs_link_bg_list(block_group, &retry_list); >> >> trace_btrfs_skip_unused_block_group(block_group); >> - spin_unlock(&block_group->lock); >> spin_unlock(&space_info->lock); >> up_write(&space_info->groups_sem); >> goto next; >> -- >> 2.49.1 >>