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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200221131124.24105-1-nborisov@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:TvtvMDtnUzlIhY9YwFEYDye3VI7Jtth4HJqcH6b88Ad8EpG/DXA w+f5aE12IE5F7k8Rr3l3ErM7ZWvU/hVceU//nCbULOEFG8hnz/kiLxxka0RLXBq5eDv+BmN +piAKI4vIDz0oKw5UWVpWC/2qdjtk9dyIAokOqorRYZbn8CCyZaB+FdEvWVvX8tQX8rYpF9 YPwMHHRNrAxJOlO9R1qfw== X-UI-Out-Filterresults: notjunk:1;V03:K0:Z9trz3Hh9wM=:fjtEn5Kbg2jM3LDhcPnis9 GzA2Jj8yXtJ6HmPqby13buL860aS9tb9XIARtp0g4W1UCNMhqn79qGvuiUlP3eov64j0zfIPk rgwVyfxA3B/sjuD9IJnUXZa7YZjLNurltY421++2pHvif2+xukNhp4+Epe0G9vIaJVNo9kxF7 ItRZH3A1diqTugB0jLLcLFyWyEZyGLs54OyhPavL7ZzMTaHbnucqYRBEauWEbjf2wSF2YMWVG MpyasDcjKGwqvwbiVExqFk2210/uM1CG5iaVI6hydlufnp4849LWdlxNGwxCBgqumBT6yaFzA KHFw9q9TtLa72xCMLZX3VLXgCYnFNQps9q8Hd/hHTOUFzpCNGu75sOJ8VI9M0a+XkGZ8L9Zba SDMBGgv4w/cMgFJAKHrJ/1Hd7Uk6M3k9PK9ztm//gASL1zvDo62kfbVF+V17KHStxabHdmPBe aFsrJplYeYadHY7RxuAI+tLe6Sq2e3lKohr3ieT5cImpREFFEdjlNw+hBvBDAFSyNty76Nlk7 8TywuvJFrik4iOOuUHQEYomAHDJiggWNj9vniFLgL4HoWy5rQ8KTwB5zHKzf1+gC2RttS0mRb cgvhIFnnOu4m0+x9TcXNe9WtzZZz4B2MBwLqG5SKGoxbrwl1CSWfS3ri5ZtohOaA0gWCvC7Yd S0ls2oKtjNNbdxv7Mv0bIUKQ/MpxUDxxMdx7YPZnvirhWe5x/sieBL3v5iyqPlFcTOZ9c9W38 /SoIraCp3r8K7kyb/Kc7sFpoRvbswVDpgg4Dj7KzVNPlZQ5rjpOpgiqjhYBTYHyBERAs7Ti5s idWWD6BkCqPMNXK1ecOOA+6b4B5Efjacih2MJZzo4Y4Z5EzPvDnu8338oTFzH1ULvb8/RmuA1 9vQCfwfXzTWgzUGo4kT5ofc6R4PqSP6o0iLY4JbkcK/P6OkHI464UMEXjp05nSadk4JqUTkn/ paEhy1QHwjCwlPT2PiwW8TjbudSeXPSc73QlCdYt8AOpWGppzS9g3FXrEqLG1p1voEPckwU3H qmWVVI+J7xFoiUSmaXb0/BSTR5Jlhzoi2naTL7IZmoYMBr9FxfH1Rhvjji6oPwPnFC/nuLVPC kv5JB0iLjTS2fJtWcxy3tkp5fX+RSvkixJI26+yxmIfQhy8KBzy+LHcsNVvYye60lQTM7R60o 5KIZMrXCS+UEPnP5oZCoskqGA8dTDL4drHKC7GUfn4Nb+BucaWNuN5R4wayLX0EZVO4xIl3Th rVmYRaqDbioLCCH+l Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2020/2/21 =E4=B8=8B=E5=8D=889:11, Nikolay Borisov wrote: > __del_reloc_root is called from: > > a) Transaction commit via: > btrfs_transaction_commit > commit_fs_roots > btrfs_update_reloc_root > __del_reloc_root > > b) From the relocation thread with the following call chains: > > relocate_block_group > merge_reloc_roots > insert_dirty_subvol > btrfs_update_reloc_root > __del_reloc_root > > c) merge_reloc_roots > free_reloc_roots > __del_reloc_roots > > (The above call chain can called from btrfs_recover_relocation as well > but for the purpose of this fix this is irrelevant). > > The commont data structure that needs protecting is > fs_info->reloc_ctl->reloc_list as reloc roots are anchored at this list. > Turns out it's no needed to hold the trans_lock in __del_reloc_root > since consistency is already guaranteed by call chain b) above holding > a transaction while calling insert_dirty_subvol, meaning we cannot have > a concurrent transaction commit. For call chain c) above a snapshot of > the fs_info->reloc_ctl->reloc_list is taken with reloc_mutex held and > free_reloc_roots is called on this local snapshot. > > Those invariants are sufficient to prevent racing calls to > __del_reloc_root alongside other users of the list, as such it's fine > to drop the lock acquisition. > > Signed-off-by: Nikolay Borisov Reviewed-by: Qu Wenruo Thanks, Qu > --- > fs/btrfs/relocation.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c > index 8076c340749f..e5cb64409f7c 100644 > --- a/fs/btrfs/relocation.c > +++ b/fs/btrfs/relocation.c > @@ -1381,9 +1381,7 @@ static void __del_reloc_root(struct btrfs_root *ro= ot) > BUG_ON((struct btrfs_root *)node->data !=3D root); > } > > - spin_lock(&fs_info->trans_lock); > list_del_init(&root->root_list); > - spin_unlock(&fs_info->trans_lock); > kfree(node); > } > >