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List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH next] btrfs: fix deadlock in btrfs_read_chunk_tree To: Hillf Danton Cc: Edward Adam Davis , syzbot+fa90fcaa28f5cd4b1fc1@syzkaller.appspotmail.com, clm@fb.com, josef@toxicpanda.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <685aa401.050a0220.2303ee.0009.GAE@google.com> <20250624235635.1661-1-hdanton@sina.com> <20250625124052.1778-1-hdanton@sina.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB 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>>>>> reported by [1]. >>>>> =3D3D20 >>>>> [1] >>>>> -> #1 (&type->s_umount_key#41/1){+.+.}-{4:4}: >>>>> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871 >>>>> down_write_nested+0x9d/0x200 kernel/locking/rwsem.c:1693 >>>>> alloc_super+0x204/0x970 fs/super.c:345 >>> =3D20 >>> Given kzalloc [3], the syzbot report is false positive (a known lockde= p >>> issue) as nobody else should acquire s->s_umount lock. >>> =3D20 >>> [3] https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-nex= t.=3D >> git/tree/fs/super.c?id=3D3D7aacdf6feed1#n319 >> >> Not a false alert either. >> >> sget_fc() can return an existing super block, we can race between a=3D2= 0 >> mount and an unmount on the same super block. >> >> In that case it's going to cause problem. >> >> This is already fixed in the v4 (and later v5) patchset: >> >> https://lore.kernel.org/linux-btrfs/cover.1750724841.git.wqu@suse.com/ >> > Can v5 survive the syzbot test? Yes, I enabled lockdep during v5 tests.