[PATCH 1/1] loop device: report mount failure in case of set_loop failure

[Thomas De Schampheleire]

Hi,

El mié, 9 dic 2020 a las 20:53, Denys Vlasenko
(<vda.linux at googlemail.com>) escribió:
>
> On Wed, Dec 9, 2020 at 10:19 AM Thomas De Schampheleire
> <patrickdepinguin at gmail.com> wrote:
> > From: Philippe Belet <philippe.belet at nokia.com>
> >
> > When mounting, in parallel, multiple loop devices (squashfs for the
> > submitter's case), the following behavior can be observed:
> >
> > stat64(/path/to/image, {st_mode=S_IFREG|0644, st_size=4096, ...}) = 0
> > openat(AT_FDCWD, /path/to/image, O_RDWR|O_LARGEFILE) = 3
> > openat(AT_FDCWD, /dev/loop-control, O_RDWR|O_LARGEFILE|O_CLOEXEC) = 4
> > ioctl(4, LOOP_CTL_GET_FREE)             = 12
> > close(4)                                = 0
> > openat(AT_FDCWD, /dev/loop12, O_RDWR|O_LARGEFILE) = 4
> > ioctl(4, LOOP_GET_STATUS64, {lo_offset=0, lo_number=12, lo_flags=LO_FLAGS_AUTOCLEAR, lo_file_name=/path/to/image, ...}) = 0
> > close(4)                                = 0
> > close(3)                                = 0
> > write(2, "mount: can't setup loop device\n", 31mount: can't setup loop device
> > ) = 31
> > exit_group(0)                           = ?
> > +++ exited with 0 +++
> >
> > The ioctl LOOP_CTL_GET_FREE has resulted in the same result for
> > a competing mount process. The subsequent ioctl LOOP_GET_STATUS64
> > fails, having succeeded for the competing mount process. Next we
> > see a series of other system calls.
> >
> > The mount code checks the errno value of the last close()
> > syscall
>
> No it does not. errno is not cleared to zero on successful syscalls,
> it's left untouched.
>
> Does just this change:
>
> -                               return errno;
> +                               return loopfd;
>
> fix the problem?


Yes, it seems so. At least with the given test program I get correct
results with this change alone.

Will you adapt directly or should I send a new patch?

Thanks,
Thomas