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Thu, 30 Jul 2026 01:36:23 -0700 (PDT) Received: from [172.16.0.229] ([159.196.52.54]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d022a16558sm22653955ad.6.2026.07.30.01.36.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jul 2026 01:36:22 -0700 (PDT) Message-ID: <30f0bdfb-c8ee-4459-8137-773020960f7b@suse.com> Date: Thu, 30 Jul 2026 18:06:17 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] iomap: follow the alignment requirement for iomap_dio_hole_iter() To: Christoph Hellwig Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org References: 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/7/30 17:15, Christoph Hellwig 写道: > On Thu, Jul 30, 2026 at 10:52:10AM +0930, Qu Wenruo wrote: >> [BUG] >> On the latest development branch, btrfs with 8K block size on 4K page >> sized systems will fail the following fsstress workload: >> >> # $fsstress -n 4 -d $mnt -s 1785675805 -v > > Please add this to xfstests. In that case I'll create a more dedicated reproducer. > >> +/* >> + * File systems that write out of place and always allocate new blocks >> + * need each bio to be block aligned as that's the unit of allocation. >> + */ >> +static unsigned int iomap_dio_alignment(const struct iomap_iter *iter, >> + const struct iomap_dio *dio) >> +{ >> + if (dio->flags & IOMAP_DIO_FSBLOCK_ALIGNED) >> + return i_blocksize(iter->inode); >> + return bdev_logical_block_size(iter->iomap.bdev); >> +} > > This already exists in the VFS iomap tree (with a slightly different > prototype). > >> static int iomap_dio_hole_iter(struct iomap_iter *iter, struct iomap_dio *dio) >> { >> - loff_t length = iov_iter_zero(iomap_length(iter), dio->submit.iter); >> + loff_t copied = iov_iter_zero(iomap_length(iter), dio->submit.iter); >> + const unsigned int alignment = iomap_dio_alignment(iter, dio); >> + const loff_t aligned_copied = round_down(copied, alignment); >> >> - dio->size += length; >> - if (!length) >> + iov_iter_revert(dio->submit.iter, copied - aligned_copied); >> + dio->size += aligned_copied; >> + if (!aligned_copied) >> return -EFAULT; >> - return iomap_iter_advance(iter, length); >> + return iomap_iter_advance(iter, aligned_copied); >> } > > iomap generall expects extents to be block aligned, how do you end up > with non-aligned reporting here? The dio read buffer is 2 pages (matching the 8K alignment), but only the first page is faulted in. Furthermore btrfs has disabled page fault during dio read, so the 2nd page will not be faulted in. Thus iov_iter_zero() only got to zero the first page. Btrfs always returned a hole that is properly aligned, but as long as bs > ps, the page fault can always break in the middle, causing unaligned range. Thanks, Qu