linux-kernel - [RFC PATCH V3 0/1] block: fix I/O errors in BLKRRPART

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Date:   Mon,  4 Jan 2021 22:06:58 +0900
From:   Minwoo Im <minwoo.im.dev@...il.com>
To:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Minwoo Im <minwoo.im.dev@...il.com>
Subject: [RFC PATCH V3 0/1] block: fix I/O errors in BLKRRPART

Hello,

  This patch fixes I/O errors during BLKRRPART ioctl() behavior right
after format operation that changed logical block size of the block
device with a same file descriptor opened.

Testcase:

  The following testcase is a case of NVMe namespace with the following
conditions:

  - Current LBA format is lbaf=0 (512 bytes logical block size)
  - LBA Format(lbaf=1) has 4096 bytes logical block size

  # Format block device logical block size 512B to 4096B
  nvme format /dev/nvme0n1 --lbaf=1 --force

  This will cause I/O errors because BLKRRPART ioctl() happened right after
the format command with same file descriptor opened in application
(e.g., nvme-cli) like:

  fd = open("/dev/nvme0n1", O_RDONLY);

  nvme_format(fd, ...);
  if (ioctl(fd, BLKRRPART) < 0)
	...

Errors:

  We can see the Read command with Number of LBA(NLB) 0xffff(65535) which
was under-flowed because BLKRRPART operation requested request size based
on i_blkbits of the block device which is 9 via buffer_head.

  [dmesg-snip]                                                                                                                              
    [   10.771740] blk_update_request: operation not supported error, dev nvme0n1, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
    [   10.780262] Buffer I/O error on dev nvme0n1, logical block 0, async page read

  [event-snip]                                                                                                                                                                                           
    kworker/0:1H-56      [000] ....   913.456922: nvme_setup_cmd: nvme0: disk=nvme0n1, qid=1, cmdid=216, nsid=1, flags=0x0, meta=0x0, cmd=(nvme_cmd_read slba=0, len=65535, ctrl=0x0, dsmgmt=0, reftag=0)
     ksoftirqd/0-9       [000] .Ns.   916.566351: nvme_complete_rq: nvme0: disk=nvme0n1, qid=1, cmdid=216, res=0x0, retries=0, flags=0x0, status=0x4002

  The patch below fixes the I/O errors by rejecting I/O requests from the
block layer with setting a flag to gendisk until the file descriptor
re-opened to be updated by __blkdev_get().  This is based on the previous
discussion [1].

Since V2:
  - Cover letter with testcase and error logs attached. Removed un-related
    changes: empty line. (Chaitanya, [2])
  - Put blkdev with blkdev_put_no_open().

Since V1:
  - Updated patch to reject I/O rather than updating i_blkbits of the
    block device's inode directly from driver. (Christoph, [1])

[1] https://lore.kernel.org/linux-nvme/20201223183143.GB13354@localhost.localdomain/T/#t
[2] https://lore.kernel.org/linux-nvme/20201230140504.GB7917@localhost.localdomain/T/#t

Thanks,

Minwoo Im (1):
  block: reject I/O for same fd if block size changed

 block/blk-settings.c    |  8 ++++++++
 block/partitions/core.c | 11 +++++++++++
 fs/block_dev.c          |  6 ++++++
 include/linux/genhd.h   |  1 +
 4 files changed, 26 insertions(+)

-- 
2.17.1