Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC patch 14/19] bpf: Use migrate_disable() in hashtab code | Date | Fri, 14 Feb 2020 20:56:12 +0100 |
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Mathieu Desnoyers <mathieu.desnoyers@efficios.com> writes: > On 14-Feb-2020 02:39:31 PM, Thomas Gleixner wrote: >> Replace the preempt_disable/enable() pairs with migrate_disable/enable() >> pairs to prepare BPF to work on PREEMPT_RT enabled kernels. On a non-RT >> kernel this maps to preempt_disable/enable(), i.e. no functional change.
...
> Having all those events randomly and silently discarded might be quite > unexpected from a user standpoint. This turns the deadlock prevention > mechanism into a random tracepoint-dropping facility, which is > unsettling.
Well, it randomly drops events which might be unrelated to the syscall target today already, this will just drop some more. Shrug.
> One alternative approach we could consider to solve this is to make > this deadlock prevention nesting counter per-thread rather than > per-cpu.
That should work both on !RT and RT.
> Also, I don't think using __this_cpu_inc() without preempt-disable or > irq off is safe. You'll probably want to move to this_cpu_inc/dec > instead, which can be heavier on some architectures.
Good catch.
Thanks,
tglx
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