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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c76916bd67dsm3129767a12.3.2026.03.29.00.03.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 29 Mar 2026 00:03:24 -0700 (PDT) Message-ID: <11c944aa-7745-4720-9f40-af99bf7bb727@suse.com> Date: Sun, 29 Mar 2026 17:33:19 +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: wait for in-flight readahead BIOs on open_ctree() error To: Teng Liu <27rabbitlt@gmail.com>, linux-btrfs@vger.kernel.org Cc: dsterba@suse.com, clm@fb.com, linux-kernel@vger.kernel.org References: <20260329063417.642647-1-27rabbitlt@gmail.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: <20260329063417.642647-1-27rabbitlt@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/3/29 17:01, Teng Liu 写道: > When open_ctree() fails during btrfs_read_chunk_tree(), readahead BIOs > submitted by readahead_tree_node_children() may still be in flight. The > error path frees fs_info without waiting for these BIOs to complete. > When a readahead BIO later completes, btrfs_simple_end_io() calls > btrfs_bio_counter_dec() which accesses the already-freed > fs_info->dev_replace.bio_counter, causing a use-after-free. > > This can be triggered by connecting a USB drive with a corrupted btrfs > filesystem (e.g. chunk tree destroyed by a partial format), where the > slow USB device keeps readahead BIOs in flight long enough for the > error path to free fs_info before they complete. It can be reproduced > on qemu with a properly corrupted btrfs img. > > BTRFS error (device sda): failed to read chunk tree: -2 > BTRFS error (device sda): open_ctree failed: -2 > BUG: unable to handle page fault for address: ffff89322ceb3000 > RIP: 0010:percpu_counter_add_batch+0xe/0xb0 > btrfs_bio_counter_sub+0x22/0x60 > btrfs_simple_end_io+0x32/0x90 > blk_update_request+0x12b/0x480 > scsi_end_request+0x26/0x1b0 > scsi_io_completion+0x50/0x790 > > Fix this by waiting for the bio_counter to reach zero in the error path > before stopping workers, so all in-flight BIOs have completed their > callbacks before fs_info is freed. The bio_counter is already > initialized in init_mount_fs_info() so this wait is safe for all error > paths reaching the fail_sb_buffer label. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=221270 > Reported-by: AHN SEOK-YOUNG > Signed-off-by: Teng Liu <27rabbitlt@gmail.com> > --- > fs/btrfs/disk-io.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index 01f2dbb69..61e6b8dca 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -3723,6 +3723,18 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device > invalidate_inode_pages2(fs_info->btree_inode->i_mapping); > > fail_sb_buffer: > + /* > + * Wait for in-flight readahead BIOs before stopping workers. > + * Readahead BIOs from btrfs_read_chunk_tree() (via > + * readahead_tree_node_children) may still be in flight on slow > + * devices (e.g. USB). Their completion callbacks > + * (btrfs_simple_end_io) access fs_info->dev_replace.bio_counter > + * which would be destroyed later, causing a use-after-free. > + * The bio_counter was already initialized in init_mount_fs_info() > + * so this wait is safe for all error paths reaching this label. > + */ > + wait_event(fs_info->dev_replace.replace_wait, > + percpu_counter_sum(&fs_info->dev_replace.bio_counter) == 0); This doesn't make any sense to me. The wait and counter are all for dev-reaplce, not matching your description of the generic metadata readahead. If you want to wait for all existing metadata reads, I didn't find a good helper, thus you will need to go through all extent buffers and wait for EXTENT_BUFFER_READING flags. > btrfs_stop_all_workers(fs_info); > btrfs_free_block_groups(fs_info); > fail_alloc: