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commite6e133c47eupstream. 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()). Fixes:8a2d71a3f2("powerpc/kprobes: Disable preemption before invoking probe handler for optprobes") Cc: stable@vger.kernel.org # v4.15+ Reported-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Acked-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.