Commits
Konrad Rzeszutek Wilk committed 466318a87f2
xen/smp: Fixup NOHZ per cpu data when onlining an offline CPU. The xen_play_dead is an undead function. When the vCPU is told to offline it ends up calling xen_play_dead wherin it calls the VCPUOP_down hypercall which offlines the vCPU. However, when the vCPU is onlined back, it resumes execution right after VCPUOP_down hypercall. That was OK (albeit the API for play_dead assumes that the CPU stays dead and never returns) but with commit 4b0c0f294 (tick: Cleanup NOHZ per cpu data on cpu down) that is no longer safe as said commit resets the ts->inidle which at the start of the cpu_idle loop was set. The net effect is that we get this warn: Broke affinity for irq 16 installing Xen timer for CPU 1 cpu 1 spinlock event irq 48 ------------[ cut here ]------------ WARNING: at /home/konrad/linux-linus/kernel/time/tick-sched.c:935 tick_nohz_idle_exit+0x195/0x1b0() Modules linked in: dm_multipath dm_mod xen_evtchn iscsi_boot_sysfs CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.10.0-rc3upstream-00068-gdcdbe33 #1 Hardware name: BIOSTAR Group N61PB-M2S/N61PB-M2S, BIOS 6.00 PG 09/03/2009 ffffffff8193b448 ffff880039da5e60 ffffffff816707c8 ffff880039da5ea0 ffffffff8108ce8b ffff880039da4010 ffff88003fa8e500 ffff880039da4010 0000000000000001 ffff880039da4000 ffff880039da4010 ffff880039da5eb0 Call Trace: [<ffffffff816707c8>] dump_stack+0x19/0x1b [<ffffffff8108ce8b>] warn_slowpath_common+0x6b/0xa0 [<ffffffff8108ced5>] warn_slowpath_null+0x15/0x20 [<ffffffff810e4745>] tick_nohz_idle_exit+0x195/0x1b0 [<ffffffff810da755>] cpu_startup_entry+0x205/0x250 [<ffffffff81661070>] cpu_bringup_and_idle+0x13/0x15 ---[ end trace 915c8c486004dda1 ]--- b/c ts_inidle is set to zero. Thomas suggested that we just add a workaround to call tick_nohz_idle_enter before returning from xen_play_dead() - and that is what this patch does and fixes the issue. We also add the stable part b/c git commit 4b0c0f294 is on the stable tree. CC: stable@vger.kernel.org Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>