* Steven Rostedt <[email protected]> wrote:
> It's still there in 2.6.15-rc1-git3 (the sem is the down_read of
> ioctl32_sem in fs/compat.c).
>
> No, the problem was unique to the rt patch. In -rt the default
> down_read is just like a down (since it is very hard to do PI on
> readers and writer locks). So the solution in -rt was to convert this
> back to a normal RW sem.
to be precise: rwsems in PREEMPT_RT are "only one reader, but reader
might self-recurse". I.e. the sequence of:
down_read();
...
down_read();
...
up_read();
...
up_read();
is still supported.
this very simple rw-semaphore type covers the overwhelming majority of
uses: out of hundreds of rwsems in the kernel, ioctl32_sem is the first
one that had to be converted to a 'compat' rwsem.
Ingo
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