Re: [RFC PATCH v2 1/3] restartable sequences: user-space per-cpu critical sections

From: Johannes Berg
Date: Thu Nov 19 2015 - 11:39:27 EST

On Tue, 2015-10-27 at 16:56 -0700, Paul Turner wrote:
> + *ÂÂflags is currently unused.
> + */
> +SYSCALL_DEFINE3(restartable_sequences,
> +> > > int, flags, long, event_and_cpu, long, post_commit_instr_addr)

> +{
> + return rseq_configure_current((__user u64 *)event_and_cpu,
> + ÂÂÂÂÂÂ(__user void *)post_commit_instr_addr);

It seems that, for forward compatibility and actually usefulness of the
'flags' argument, you need to reject the syscall if it's passed non-
zero right now. Otherwise applications can (inadvertedly) pass garbage
and you'll not be able to use it in the future.

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