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From: Mikulas Patocka <mpatocka@redhat.com>
To: Milan Broz <gmazyland@gmail.com>,
	Bart Van Assche <bvanassche@acm.org>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Changheun Lee <nanich.lee@samsung.com>
Cc: alex_y_xu@yahoo.ca, axboe@kernel.dk, bgoncalv@redhat.com,
	dm-crypt@saout.de, hch@lst.de, jaegeuk@kernel.org,
	linux-block@vger.kernel.org, linux-ext4@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	ming.lei@redhat.com, yi.zhang@redhat.com, dm-devel@redhat.com
Subject: Re: regression: data corruption with ext4 on LUKS on nvme with torvalds master
Date: Thu, 13 May 2021 15:22:25 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LRH.2.02.2105131510330.21927@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <0e7b0b6e-e78c-f22d-af8d-d7bdcb597bea@gmail.com>



> On 5/13/21 7:15 AM, Theodore Ts'o wrote:
> > On Thu, May 13, 2021 at 06:42:22PM +0900, Changheun Lee wrote:
> >>
> >> Problem might be casued by exhausting of memory. And memory exhausting
> >> would be caused by setting of small bio_max_size. Actually it was not
> >> reproduced in my VM environment at first. But, I reproduced same problem
> >> when bio_max_size is set with 8KB forced. Too many bio allocation would
> >> be occurred by setting of 8KB bio_max_size.
> > 
> > Hmm... I'm not sure how to align your diagnosis with the symptoms in
> > the bug report.  If we were limited by memory, that should slow down
> > the I/O, but we should still be making forward progress, no?  And a
> > forced reboot should not result in data corruption, unless maybe there
> > was a missing check for a failed memory allocation, causing data to be
> > written to the wrong location, a missing error check leading to the
> > block or file system layer not noticing that a write had failed
> > (although again, memory exhaustion should not lead to failed writes;
> > it might slow us down, sure, but if writes are being failed, something
> > is Badly Going Wrong --- things like writes to the swap device or
> > writes by the page cleaner must succeed, or else Things Would Go Bad
> > In A Hurry).
> 
> After the LUKS data corruption issue was reported I decided to take a
> look at the dm-crypt code. In that code I found the following:
> 
> static void clone_init(struct dm_crypt_io *io, struct bio *clone)
> {
> 	struct crypt_config *cc = io->cc;
> 
> 	clone->bi_private = io;
> 	clone->bi_end_io  = crypt_endio;
> 	bio_set_dev(clone, cc->dev->bdev);
> 	clone->bi_opf	  = io->base_bio->bi_opf;
> }
> [ ... ]
> static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned size)
> {
> 	[ ... ]
> 	clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, &cc->bs);
> 	[ ... ]
> 	clone_init(io, clone);
> 	[ ... ]
> 	for (i = 0; i < nr_iovecs; i++) {
> 		[ ... ]
> 		bio_add_page(clone, page, len, 0);
> 
> 		remaining_size -= len;
> 	}
> 	[ ... ]
> }
> 
> My interpretation is that crypt_alloc_buffer() allocates a bio,
> associates it with the underlying device and clones a bio. The input bio
> may have a size up to UINT_MAX while the new limit for the size of the
> cloned bio is max_sectors * 512. That causes bio_add_page() to fail if
> the input bio is larger than max_sectors * 512, hence the data
> corruption. Please note that this is a guess only and that I'm not
> familiar with the dm-crypt code.
> 
> Bart.

We already had problems with too large bios in dm-crypt and we fixed it by 
adding this piece of code:

        /*
         * Check if bio is too large, split as needed.
         */
        if (unlikely(bio->bi_iter.bi_size > (BIO_MAX_VECS << PAGE_SHIFT)) &&
            (bio_data_dir(bio) == WRITE || cc->on_disk_tag_size))
                dm_accept_partial_bio(bio, ((BIO_MAX_VECS << PAGE_SHIFT) >> SECTOR_SHIFT));

It will ask the device mapper to split the bio if it is too large. So, 
crypt_alloc_buffer can't receive a bio that is larger than BIO_MAX_VECS << 
PAGE_SHIFT.

Mikulas


  parent reply	other threads:[~2021-05-13 19:22 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20210513100034epcas1p4b23892cd77bde73c777eea6dc51c16a4@epcas1p4.samsung.com>
2021-05-13  9:42 ` regression: data corruption with ext4 on LUKS on nvme with torvalds master Changheun Lee
2021-05-13 14:15   ` Theodore Ts'o
2021-05-13 15:59     ` Bart Van Assche
     [not found]       ` <0e7b0b6e-e78c-f22d-af8d-d7bdcb597bea@gmail.com>
2021-05-13 19:22         ` Mikulas Patocka [this message]
2021-05-13 21:18           ` Bart Van Assche
2021-05-14  9:43             ` Mikulas Patocka
2021-05-14  9:50           ` Mikulas Patocka
     [not found]             ` <CGME20210514104426epcas1p3ee2f22f8e18c961118795c356e6a14ae@epcas1p3.samsung.com>
2021-05-14 10:26               ` Changheun Lee
2021-07-09 20:45                 ` Samuel Mendoza-Jonas
     [not found] <1620493841.bxdq8r5haw.none.ref@localhost>
2021-05-08 17:54 ` Alex Xu (Hello71)
2021-05-09  2:29   ` Alex Xu (Hello71)
2021-05-09  3:51     ` Jens Axboe
2021-05-09 14:47       ` Alex Xu (Hello71)

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