Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Fri, May 31, 2019 at 03:20:12PM +0100, David Howells wrote:
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> > (and it has already been established that refcount_t doesn't work for
> > usage count scenarios)
> 
> ?
> 
> Does that mean struct kref doesn't either?

Indeed, since kref is just a pointless wrapper around refcount_t it does
not either.

The main distinction between a reference count and a usage count is that
0 means different things. For a refcount 0 means dead. For a usage count
0 is merely unused but valid.

Incrementing a 0 refcount is a serious bug -- use-after-free (and hence
refcount_t will refuse this and splat), for a usage count this is no
problem.

Now, it is sort-of possible to merge the two, by basically stating
something like: usage = refcount - 1. But that can get tricky and people
have not really liked the result much for the few times I tried.



[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]

  Powered by Linux