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(2403-580d-fda1-0-2bb5-f164-6e6a-38d8.ip6.aussiebb.net. [2403:580d:fda1:0:2bb5:f164:6e6a:38d8]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c433557c47sm6928115ad.79.2026.06.11.22.24.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Jun 2026 22:24:26 -0700 (PDT) Message-ID: Date: Fri, 12 Jun 2026 14:54:22 +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: Direct IO page bouncing got some garbage? From: Qu Wenruo To: linux-btrfs , "linux-fsdevel@vger.kernel.org" , "linux-block@vger.kernel.org" , Linux Memory Management List References: Content-Language: en-US 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 2026/6/12 11:11, Qu Wenruo 写道: > Hi, > > Recently I'm trying to make btrfs utilize IOMAP_DIO_BOUNCE, however I'm > experiencing weird data corruption. > > During test case generic/708, I'm reliably hitting garbage pages at the > last 64KiB, the garbage even contains an ELF header. Added ftrace shows that, since btrfs has to disable page fault to avoid certain deadlock, bio_iov_iter_bounced() failed with a short copy. Initially bio_iov_iter_bounced() got a 1MiB page, but copy_iter_from() only copied 64K then failed due to the disabled page fault. I don't think it's a coincident that the short 64K exactly matches where the garbage is (the last 64K). I guess it's in the error path we didn't properly revert the iov iter? > > In that test case, we mmap a 2MiB sized buffer from another file, and > use that 2MiB mmapped memory as buffer for direct IO, write into a > different file. > > The source file has dirty page cache for that 2MiB range, and no > writeback happened during that direct IO write. > > So it means as long as we fault in all the pages of that 2MiB buffer, we > should be able to copy them into the newly allocated folio, and submit a > bio using the bounced pages. > > But the last 64KiB is reliably corrupted with some ELF header. > > I'm wondering where the corruption is from, especially it seems btrfs > has very little to do, except calling fault_in_iov_readable() to fault > in all the pages. > > Thanks, > Qu