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From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <tom.leiming@gmail.com>
Cc: Eric Biggers <ebiggers@kernel.org>,
	Ming Lei <ming.lei@redhat.com>,
	"open list:AIO" <linux-aio@kvack.org>,
	linux-block <linux-block@vger.kernel.org>,
	linux-api@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Jeff Moyer <jmoyer@redhat.com>, Avi Kivity <avi@scylladb.com>,
	jannh@google.com, Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio
Date: Tue, 26 Feb 2019 18:47:54 -0700
Message-ID: <09820845-07cb-5153-e1c5-59ed185db26f@kernel.dk> (raw)
In-Reply-To: <CACVXFVNOFA8_p+hVvaCffWAQ7+dgn++0b4Wn3naJzyNZN=CoFg@mail.gmail.com>

On 2/26/19 6:21 PM, Ming Lei wrote:
> On Tue, Feb 26, 2019 at 11:56 PM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On 2/25/19 9:34 PM, Jens Axboe wrote:
>>> On 2/25/19 8:46 PM, Eric Biggers wrote:
>>>> Hi Jens,
>>>>
>>>> On Thu, Feb 21, 2019 at 10:45:27AM -0700, Jens Axboe wrote:
>>>>> On 2/20/19 3:58 PM, Ming Lei wrote:
>>>>>> On Mon, Feb 11, 2019 at 12:00:41PM -0700, Jens Axboe wrote:
>>>>>>> For an ITER_BVEC, we can just iterate the iov and add the pages
>>>>>>> to the bio directly. This requires that the caller doesn't releases
>>>>>>> the pages on IO completion, we add a BIO_NO_PAGE_REF flag for that.
>>>>>>>
>>>>>>> The current two callers of bio_iov_iter_get_pages() are updated to
>>>>>>> check if they need to release pages on completion. This makes them
>>>>>>> work with bvecs that contain kernel mapped pages already.
>>>>>>>
>>>>>>> Reviewed-by: Hannes Reinecke <hare@suse.com>
>>>>>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>>>>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>>>>> ---
>>>>>>>  block/bio.c               | 59 ++++++++++++++++++++++++++++++++-------
>>>>>>>  fs/block_dev.c            |  5 ++--
>>>>>>>  fs/iomap.c                |  5 ++--
>>>>>>>  include/linux/blk_types.h |  1 +
>>>>>>>  4 files changed, 56 insertions(+), 14 deletions(-)
>>>>>>>
>>>>>>> diff --git a/block/bio.c b/block/bio.c
>>>>>>> index 4db1008309ed..330df572cfb8 100644
>>>>>>> --- a/block/bio.c
>>>>>>> +++ b/block/bio.c
>>>>>>> @@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page,
>>>>>>>  }
>>>>>>>  EXPORT_SYMBOL(bio_add_page);
>>>>>>>
>>>>>>> +static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
>>>>>>> +{
>>>>>>> + const struct bio_vec *bv = iter->bvec;
>>>>>>> + unsigned int len;
>>>>>>> + size_t size;
>>>>>>> +
>>>>>>> + len = min_t(size_t, bv->bv_len, iter->count);
>>>>>>> + size = bio_add_page(bio, bv->bv_page, len,
>>>>>>> +                         bv->bv_offset + iter->iov_offset);
>>>>>>
>>>>>> iter->iov_offset needs to be subtracted from 'len', looks
>>>>>> the following delta change[1] is required, otherwise memory corruption
>>>>>> can be observed when running xfstests over loop/dio.
>>>>>
>>>>> Thanks, I folded this in.
>>>>>
>>>>> --
>>>>> Jens Axboe
>>>>>
>>>>
>>>> syzkaller started hitting a crash on linux-next starting with this commit, and
>>>> it still occurs even with your latest version that has Ming's fix folded in.
>>>> Specifically, commit a566653ab5ab80a from your io_uring branch with commit date
>>>> Sun Feb 24 08:20:53 2019 -0700.
>>>>
>>>> Reproducer:
>>>>
>>>> #define _GNU_SOURCE
>>>> #include <fcntl.h>
>>>> #include <linux/loop.h>
>>>> #include <sys/ioctl.h>
>>>> #include <sys/sendfile.h>
>>>> #include <sys/syscall.h>
>>>> #include <unistd.h>
>>>>
>>>> int main(void)
>>>> {
>>>>         int memfd, loopfd;
>>>>
>>>>         memfd = syscall(__NR_memfd_create, "foo", 0);
>>>>
>>>>         pwrite(memfd, "\xa8", 1, 4096);
>>>>
>>>>         loopfd = open("/dev/loop0", O_RDWR|O_DIRECT);
>>>>
>>>>         ioctl(loopfd, LOOP_SET_FD, memfd);
>>>>
>>>>         sendfile(loopfd, loopfd, NULL, 1000000);
>>>> }
>>>>
>>>>
>>>> Crash:
>>>>
>>>> page:ffffea0001a6aab8 count:0 mapcount:0 mapping:0000000000000000 index:0x0
>>>> flags: 0x100000000000000()
>>>> raw: 0100000000000000 ffffea0001ad2c50 ffff88807fca49d0 0000000000000000
>>>> raw: 0000000000000000 0000000000000000 00000000ffffffff
>>>> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0)
>>>
>>> I see what this is, I'll cut a fix for this tomorrow.
>>
>> Folded in a fix for this, it's in my current io_uring branch and my for-next
>> branch.
> 
> Hi Jens,
> 
> I saw the following change is added:
> 
> + if (size == len) {
> + /*
> + * For the normal O_DIRECT case, we could skip grabbing this
> + * reference and then not have to put them again when IO
> + * completes. But this breaks some in-kernel users, like
> + * splicing to/from a loop device, where we release the pipe
> + * pages unconditionally. If we can fix that case, we can
> + * get rid of the get here and the need to call
> + * bio_release_pages() at IO completion time.
> + */
> + get_page(bv->bv_page);
> 
> Now the 'bv' may point to more than one page, so the following one may be
> needed:
> 
> int i;
> struct bvec_iter_all iter_all;
> struct bio_vec *tmp;
> 
> mp_bvec_for_each_segment(tmp, bv, i, iter_all)
>       get_page(tmp->bv_page);

I guess that would be the safest, even if we don't currently have more
than one page in there. I'll fix it up.

-- 
Jens Axboe


  reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11 19:00 [PATCHSET v15] io_uring IO interface Jens Axboe
2019-02-11 19:00 ` [PATCH 01/19] fs: add an iopoll method to struct file_operations Jens Axboe
2019-02-11 19:00 ` [PATCH] io_uring: add io_uring_event cache hit information Jens Axboe
2019-02-11 19:00 ` [PATCH 02/19] block: wire up block device iopoll method Jens Axboe
2019-02-11 19:00 ` [PATCH 03/19] block: add bio_set_polled() helper Jens Axboe
2019-02-11 19:00 ` [PATCH 04/19] iomap: wire up the iopoll method Jens Axboe
2019-02-11 19:00 ` [PATCH 05/19] Add io_uring IO interface Jens Axboe
2019-02-11 19:00 ` [PATCH 06/19] io_uring: add fsync support Jens Axboe
2019-02-11 19:00 ` [PATCH 07/19] io_uring: support for IO polling Jens Axboe
2019-02-11 19:00 ` [PATCH 08/19] fs: add fget_many() and fput_many() Jens Axboe
2019-02-11 19:00 ` [PATCH 09/19] io_uring: use fget/fput_many() for file references Jens Axboe
2019-02-11 19:00 ` [PATCH 10/19] io_uring: batch io_kiocb allocation Jens Axboe
2019-02-11 19:00 ` [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Jens Axboe
2019-02-20 22:58   ` Ming Lei
2019-02-21 17:45     ` Jens Axboe
2019-02-26  3:46       ` Eric Biggers
2019-02-26  4:34         ` Jens Axboe
2019-02-26 15:54           ` Jens Axboe
2019-02-27  1:21             ` Ming Lei
2019-02-27  1:47               ` Jens Axboe [this message]
2019-02-27  1:53                 ` Ming Lei
2019-02-27  1:57                   ` Jens Axboe
2019-02-27  2:21                     ` Ming Lei
2019-02-27  2:28                       ` Jens Axboe
2019-02-27  2:37                         ` Ming Lei
2019-02-27  2:43                           ` Jens Axboe
2019-02-27  3:09                             ` Ming Lei
2019-02-27  3:37                               ` Jens Axboe
2019-02-27  3:43                                 ` Jens Axboe
2019-02-27  3:44                                 ` Ming Lei
2019-02-27  4:05                                   ` Jens Axboe
2019-02-27  4:06                                     ` Jens Axboe
2019-02-27 19:42                                       ` Christoph Hellwig
2019-02-28  8:37                                         ` Ming Lei
2019-02-27 23:35                         ` Ming Lei
2019-03-08  7:55                         ` Christoph Hellwig
2019-03-08  9:12                           ` Ming Lei
2019-03-08  8:18                     ` Christoph Hellwig
2019-02-11 19:00 ` [PATCH 12/19] io_uring: add support for pre-mapped user IO buffers Jens Axboe
2019-02-19 19:08   ` Jann Horn
2019-02-22 22:29     ` Jens Axboe
2019-02-11 19:00 ` [PATCH 13/19] net: split out functions related to registering inflight socket files Jens Axboe
2019-02-11 19:00 ` [PATCH 14/19] io_uring: add file set registration Jens Axboe
2019-02-19 16:12   ` Jann Horn
2019-02-22 22:29     ` Jens Axboe
2019-02-11 19:00 ` [PATCH 15/19] io_uring: add submission polling Jens Axboe
2019-02-11 19:00 ` [PATCH 16/19] io_uring: add io_kiocb ref count Jens Axboe
2019-02-11 19:00 ` [PATCH 17/19] io_uring: add support for IORING_OP_POLL Jens Axboe
2019-02-11 19:00 ` [PATCH 18/19] io_uring: allow workqueue item to handle multiple buffered requests Jens Axboe
2019-02-11 19:00 ` [PATCH 19/19] io_uring: add io_uring_event cache hit information Jens Axboe
2019-02-21 12:10 ` [PATCHSET v15] io_uring IO interface Marek Majkowski
2019-02-21 17:48   ` Jens Axboe
2019-02-22 15:01     ` Marek Majkowski
2019-02-22 22:32       ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2019-02-09 21:13 [PATCHSET v14] " Jens Axboe
2019-02-09 21:13 ` [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Jens Axboe
2019-02-08 17:34 [PATCHSET v13] io_uring IO interface Jens Axboe
2019-02-08 17:34 ` [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Jens Axboe
2019-02-09  9:45   ` Hannes Reinecke

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