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Subject: Re: Warning when using eMMC and partprobe: generic_make_request:
 Trying to write to read-only block-device
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Ilya Dryomov <idryomov@gmail.com>
Cc:     stefan@agner.ch, Sagi Grimberg <sagi@grimberg.me>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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 <CA+55aFwyCmYfUrGt61d-6B=1XiTLoudNO=_bQ9-g_rDg8Ao_VA@mail.gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <22fff85b-63e5-3cfe-0e72-255044e53bab@kernel.dk>
Date:   Tue, 14 Aug 2018 10:24:47 -0600
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On 8/14/18 10:22 AM, Linus Torvalds wrote:
> On Tue, Aug 14, 2018 at 8:24 AM Ilya Dryomov <idryomov@gmail.com> wrote:
>>
>> Looks like it's coming from that fsync():
>>
>>   sys_fsync
>>     do_fsync
>>       vfs_fsync_range
>>         blkdev_fsync
>>           blkdev_issue_flush
>>
>> I think we need to teach blkdev_issue_flush() to bail out if the bdev
>> is read-only, similar to blkdev_issue_discard(), _write_zeroes(), etc.
>> The question is which error code to use.  blkdev_fsync() already skips
>> over EOPNOTSUPP, so it is a (no-so-good) option.  Other blkdev_issue_
>> functions return EPERM.
> 
> Oh, just make issue_flush() return EROFS for a read-only device.
> 
> Or maybe we should even just consider the flush to be a read operation?
> 
> But I guess the error code gets percolated all the way to user space?
> The safest option might just be to return 0.

We probably just want to special case a flush for this check. In other
situations, like resource allocation and issue, we'd want to consider
it a write.

-- 
Jens Axboe