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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30f0bbd2362sm42503849eec.20.2026.07.04.22.57.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 04 Jul 2026 22:58:02 -0700 (PDT) Message-ID: <7fd6b604-ca23-4881-8727-43a98aa0521a@suse.com> Date: Sun, 5 Jul 2026 15:27:57 +0930 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 v2] btrfs: fix extent map leak in NOCOW direct I/O write To: Shuangpeng Bai , linux-btrfs@vger.kernel.org Cc: linux-kernel@vger.kernel.org, clm@fb.com, dsterba@suse.com, fdmanana@suse.com, jbacik@fb.com, stable@vger.kernel.org References: <20260705054637.80584-1-shuangpeng.kernel@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: <20260705054637.80584-1-shuangpeng.kernel@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/7/5 15:16, Shuangpeng Bai 写道: > btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an > extent map reference that must be dropped on all exit paths. > > For direct writes into a NOCOW range, btrfs_get_blocks_direct_write() > keeps using that extent map and asks btrfs_create_dio_extent() to > allocate the ordered extent. If that fails, for example because > btrfs_alloc_ordered_extent() fails, the function returns the error > without dropping the input extent map. The PREALLOC path avoided this by > dropping the input extent map before replacing it with the newly > created one. > > Check the error from btrfs_create_dio_extent() before replacing the > map and drop the input extent map on failure. > > Fixes: 5f9a8a51d8b9 ("Btrfs: add semaphore to synchronize direct IO writes with fsync") > Cc: stable@vger.kernel.org > Signed-off-by: Shuangpeng Bai Reviewed-by: Qu Wenruo Thanks, Qu > --- > Changes since v1: > - Add a comment explaining the returned @em2 pointer. > - Use @em2 to decide whether to replace the old extent map and assert > that this only happens for PREALLOC writes. > > fs/btrfs/direct-io.c | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > > diff --git a/fs/btrfs/direct-io.c b/fs/btrfs/direct-io.c > index 460326d34143..19a1259b3b2f 100644 > --- a/fs/btrfs/direct-io.c > +++ b/fs/btrfs/direct-io.c > @@ -281,17 +281,24 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map, > em2 = btrfs_create_dio_extent(BTRFS_I(inode), dio_data, start, > &file_extent, type); > btrfs_dec_nocow_writers(bg); > - if (type == BTRFS_ORDERED_PREALLOC) { > - btrfs_free_extent_map(em); > - *map = em2; > - em = em2; > - } > - > if (IS_ERR(em2)) { > ret = PTR_ERR(em2); > + btrfs_free_extent_map(em); > + *map = NULL; > goto out; > } > > + /* > + * True NOCOW writes don't need to create a new extent map, > + * while PREALLOC writes must replace the existing one. > + */ > + if (em2) { > + ASSERT(type == BTRFS_ORDERED_PREALLOC); > + btrfs_free_extent_map(em); > + *map = em2; > + em = em2; > + } > + > dio_data->nocow_done = true; > } else { > /* Our caller expects us to free the input extent map. */