Re: [PATCH] proc: nommu: /proc/<pid>/maps: release mmap read lock

[Ben Wolsieffer]

On Thu, Sep 14, 2023 at 10:02:03AM -0700, Andrew Morton wrote:
> On Thu, 14 Sep 2023 12:30:20 -0400 Ben Wolsieffer <ben.wolsieffer@xxxxxxxxxxx> wrote:
> 
> > The no-MMU implementation of /proc/<pid>/map doesn't normally release
> > the mmap read lock, because it uses !IS_ERR_OR_NULL(_vml) to determine
> > whether to release the lock. Since _vml is NULL when the end of the
> > mappings is reached, the lock is not released.
> > 
> 
> Thanks.  Is this bug demonstrable from userspace?  If so, how?

Yes, run "cat /proc/1/maps" twice. You should observe that the
second run hangs.