Messages in this thread | | | Date | Sun, 19 Apr 2015 07:08:23 -0700 | From | Guenter Roeck <> | Subject | Re: qemu:arm test failure due to commit 8053871d0f7f (smp: Fix smp_call_function_single_async() locking) |
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On 04/19/2015 02:31 AM, Ingo Molnar wrote: > > * Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> On Sun, Apr 19, 2015 at 4:48 AM, Linus Torvalds >> <torvalds@linux-foundation.org> wrote: >>> >>> Does that smaller patch work equally well? >> >> .. and here's a properly formatted email and patch. >> >> Linus > >> kernel/smp.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/smp.c b/kernel/smp.c >> index 2aaac2c47683..07854477c164 100644 >> --- a/kernel/smp.c >> +++ b/kernel/smp.c >> @@ -159,8 +159,10 @@ static int generic_exec_single(int cpu, struct call_single_data *csd, >> } >> >> >> - if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) >> + if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) { >> + csd_unlock(csd); >> return -ENXIO; >> + } > > Acked-by: Ingo Molnar <mingo@kernel.org> > Tested-by: Guenter Roeck <linux@roeck-us.net>
> Btw., in this case we should probably also generate a WARN_ONCE() > warning? > > I _think_ most such callers calling an SMP function call for offline > or out of range CPUs are at minimum racy. > Not really; at least the online cpu part is an absolutely normal use case for qemu-arm.
Sure, you can argue that "this isn't the real system", and that qemu-arm should be "fixed", but there are reasons - the emulation is (much) slower if the number of CPUs is set to 4, and not everyone who wants to use qemu has a system with as many CPUs as the emulated system would normally have.
Thanks, Guenter
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