Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch V2 4/9] softirq: Make softirq control and processing RT aware | Date | Wed, 09 Dec 2020 13:36:54 +0100 |
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On Wed, Dec 09 2020 at 11:11, Peter Zijlstra wrote: > On Fri, Dec 04, 2020 at 06:01:55PM +0100, Thomas Gleixner wrote: >> From: Thomas Gleixner <tglx@linutronix.de> >> + /* First entry of a task into a BH disabled section? */ >> + if (!current->softirq_disable_cnt) { >> + if (preemptible()) { >> + local_lock(&softirq_ctrl.lock); > > AFAICT this significantly changes the locking rules. > > Where previously we could do: > > spin_lock(&ponies) > spin_lock_bh(&foo); > > vs > > spin_lock_bh(&bar); > spin_lock(&ponies) > > provided the rest of the code observed: bar -> ponies -> foo > and never takes ponies from in-softirq. > > This is now a genuine deadlock on RT.
I know, but making this work is trying to square the circle.
Any approach we tried before going this way had worse problems than this particular limitation.
> Also see: > > https://lkml.kernel.org/r/X9CheYjuXWc75Spa@hirez.programming.kicks-ass.net
I'm aware of that and it's fortunately not that many instances of this.
Thanks,
tglx
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