Revert "x86/entry: Fix the end of the stack for newly forked tasks" (ebd57499) · Commits · 戴 / test

Petr Mladek reported the following warning when loading the livepatch sample module: WARNING: CPU: 1 PID: 3699 at arch/x86/kernel/stacktrace.c:132 save_stack_trace_tsk_reliable+0x133/0x1a0 ... Call Trace: __schedule+0x273/0x820 schedule+0x36/0x80 kthreadd+0x305/0x310 ? kthread_create_on_cpu+0x80/0x80 ? icmp_echo.part.32+0x50/0x50 ret_from_fork+0x2c/0x40 That warning means the end of the stack is no longer recognized as such for newly forked tasks. The problem was introduced with the following commit: ("x86/entry: Fix the end of the stack for newly forked tasks") ... which was completely misguided. It only partially fixed the reported issue, and it introduced another bug in the process. None of the other entry code saves the frame pointer before calling into C code, so it doesn't make sense for ret_from_fork to do so either. Contrary to what I originally thought, the original issue wasn't related to newly forked tasks. It was actually related to ftrace. When entry code calls into a function which then calls into an ftrace handler, the stack frame looks different than normal. The original issue will be fixed in the unwinder, in a subsequent patch. Reported-by:

Petr Mladek <pmladek@suse.com> Signed-off-by:

Josh Poimboeuf <jpoimboe@redhat.com> Acked-by:

Thomas Gleixner <tglx@linutronix.de> Cc: Dave Jones <davej@codemonkey.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: live-patching@vger.kernel.org Fixes: ("x86/entry: Fix the end of the stack for newly forked tasks") Link: http://lkml.kernel.org/r/f350760f7e82f0750c8d1dd093456eb212751caa.1495553739.git.jpoimboe@redhat.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_32.S

+19 −11

Original line number	Diff line number	Diff line
		@@ -251,6 +251,23 @@ ENTRY(__switch_to_asm)
		jmp __switch_to
		END(__switch_to_asm)

		/*
		* The unwinder expects the last frame on the stack to always be at the same
		* offset from the end of the page, which allows it to validate the stack.
		* Calling schedule_tail() directly would break that convention because its an
		* asmlinkage function so its argument has to be pushed on the stack. This
		* wrapper creates a proper "end of stack" frame header before the call.
		*/
		ENTRY(schedule_tail_wrapper)
		FRAME_BEGIN

		pushl %eax
		call schedule_tail
		popl %eax

		FRAME_END
		ret
		ENDPROC(schedule_tail_wrapper)
		/*
		* A newly forked process directly context switches into this address.
		*
		@@ -259,24 +276,15 @@ END(__switch_to_asm)
		* edi: kernel thread arg
		*/
		ENTRY(ret_from_fork)
		FRAME_BEGIN /* help unwinder find end of stack */

		/*
		* schedule_tail() is asmlinkage so we have to put its 'prev' argument
		* on the stack.
		*/
		pushl %eax
		call schedule_tail
		popl %eax
		call schedule_tail_wrapper

		testl %ebx, %ebx
		jnz 1f /* kernel threads are uncommon */

		2:
		/* When we fork, we trace the syscall return in the child, too. */
		leal FRAME_OFFSET(%esp), %eax
		movl %esp, %eax
		call syscall_return_slowpath
		FRAME_END
		jmp restore_all

		/* kernel thread */

arch/x86/entry/entry_64.S

+4 −7

Original line number	Diff line number	Diff line
		@@ -36,7 +36,6 @@
		#include <asm/smap.h>
		#include <asm/pgtable_types.h>
		#include <asm/export.h>
		#include <asm/frame.h>
		#include <linux/err.h>

		.code64
		@@ -406,7 +405,6 @@ END(__switch_to_asm)
		* r12: kernel thread arg
		*/
		ENTRY(ret_from_fork)
		FRAME_BEGIN /* help unwinder find end of stack */
		movq %rax, %rdi
		call schedule_tail /* rdi: 'prev' task parameter */

		@@ -414,11 +412,10 @@ ENTRY(ret_from_fork)
		jnz 1f /* kernel threads are uncommon */

		2:
		leaq FRAME_OFFSET(%rsp),%rdi /* pt_regs pointer */
		movq %rsp, %rdi
		call syscall_return_slowpath /* returns with IRQs disabled */
		TRACE_IRQS_ON /* user mode is traced as IRQS on */
		SWAPGS
		FRAME_END
		jmp restore_regs_and_iret

		1:

Admin message