On Wed, Jan 17, 2018 at 05:52:24PM +0530, Naveen N. Rao wrote: > Michael Ellerman reported the following call trace when running > ftracetest: > > BUG: using __this_cpu_write() in preemptible [00000000] code: ftracetest/6178 > caller is opt_pre_handler+0xc4/0x110 > CPU: 1 PID: 6178 Comm: ftracetest Not tainted 4.15.0-rc7-gcc6x-gb2cd1df #1 > Call Trace: > [c0000000f9ec39c0] [c000000000ac4304] dump_stack+0xb4/0x100 (unreliable) > [c0000000f9ec3a00] [c00000000061159c] check_preemption_disabled+0x15c/0x170 > [c0000000f9ec3a90] [c000000000217e84] opt_pre_handler+0xc4/0x110 > [c0000000f9ec3af0] [c00000000004cf68] optimized_callback+0x148/0x170 > [c0000000f9ec3b40] [c00000000004d954] optinsn_slot+0xec/0x10000 > [c0000000f9ec3e30] [c00000000004bae0] kretprobe_trampoline+0x0/0x10 > > This is showing up since OPTPROBES is now enabled with CONFIG_PREEMPT. > > trampoline_probe_handler() considers itself to be a special kprobe > handler for kretprobes. In doing so, it expects to be called from > kprobe_handler() on a trap, and re-enables preemption before returning a > non-zero return value so as to suppress any subsequent processing of the > trap by the kprobe_handler(). > > However, with optprobes, we don't deal with special handlers (we ignore > the return code) and just try to re-enable preemption causing the above > trace. > > To address this, modify trampoline_probe_handler() to not be special. > The only additional processing done in kprobe_handler() is to emulate > the instruction (in this case, a 'nop'). We adjust the value of > regs->nip for the purpose and delegate the job of re-enabling > preemption and resetting current kprobe to the probe handlers > (kprobe_handler() or optimized_callback()). > > Reported-by: Michael Ellerman <m...@ellerman.id.au> > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ana...@linux.vnet.ibm.com>
