Hi Will, On Fri, Feb 01, 2019 at 10:19:19AM +0000, Will Deacon wrote: > Hi Russell, > > On Fri, Jan 25, 2019 at 09:03:57PM +0000, Russell King wrote: > > Executing loops such as: > > > > while (1) > > cpu_relax(); > > > > with interrupts disabled results in a livelock of the entire system, > > as other CPUs are prevented making progress. This is most noticable > > as a failure of crashdump kexec, which stops just after issuing: > > > > Loading crashdump kernel... > > > > to the system console. A workaround for this is to use 10 nops in > > cpu_relax(). > > > > We also use wfe() in while (1) loops to avoid burning cycles in a > > tight loop, giving the CPU a hint that we're not doing anything > > useful. > > > > Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx> > > --- > > It's been a while since this was posted, Will's suggestion was to use > > 10 nops in cpu_relax() last time around. I still prefer wfe() in > > these infinite-not-doing-anything-ever loops. > > > > arch/arm/include/asm/barrier.h | 2 ++ > > arch/arm/include/asm/processor.h | 6 +++++- > > arch/arm/kernel/machine_kexec.c | 5 ++++- > > arch/arm/kernel/smp.c | 4 +++- > > arch/arm/mach-omap2/prm_common.c | 4 +++- > > 5 files changed, 17 insertions(+), 4 deletions(-) > > Thanks, this looks good to me and your explanation later in the thread makes > a lot of sense: > > Acked-by: Will Deacon <will.deacon@xxxxxxx> > > Feel free to put some of the erratum writeup that I shared in the commit > message, if you like. I think it may make more sense to use my writeup as a basis for a better commit log that explains why we're doing what we're doing. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up
