Linus Torvalds 0f1f692375 While rewriting the function graph tracer, I discovered a design flaw that ... was introduced by a patch that tried to fix one bug, but by doing so created another bug. As both bugs corrupt the output (but they do not crash the kernel), I decided to fix the design such that it could have both bugs fixed. The original fix, fixed time reporting of the function graph tracer when doing a max_depth of one. This was code that can test how much the kernel interferes with userspace. But in doing so, it could corrupt the time keeping of the function profiler. The issue is that the curr_ret_stack variable was being used for two different meanings. One was to keep track of the stack pointer on the ret_stack (shadow stack used by the function graph tracer), and the other use case was the graph call depth. Although, the two may be closely related, where they got updated was the issue that lead to the two different bugs that required the two use cases to be updated differently. The big issue with this fix is that it requires changing each architecture. The good news is, I was able to remove a lot of code that was duplicated within the architectures and place it into a single location. Then I could make the fix in one place. I pushed this code into linux-next to let it settle over a week, and before doing so, I cross compiled all the affected architectures to make sure that they built fine. In the mean time, I also pulled in a patch that fixes the sched_switch previous tasks state output, that was not actually correct. -----BEGIN PGP SIGNATURE----- iIoEABYIADIWIQRRSw7ePDh/lE+zeZMp5XQQmuv6qgUCW/4NPhQccm9zdGVkdEBn b29kbWlzLm9yZwAKCRAp5XQQmuv6qnWAAQCyUIRLgYImr81eTl52lxNRsULk+aiI U29kRFWWU0c40AEA1X9sDF0MgOItbRGfZtnHTZEousXRDaDf4Fge2kF7Egg= =liQ0 -----END PGP SIGNATURE----- Merge tag 'trace-v4.20-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull tracing fixes from Steven Rostedt: "While rewriting the function graph tracer, I discovered a design flaw that was introduced by a patch that tried to fix one bug, but by doing so created another bug. As both bugs corrupt the output (but they do not crash the kernel), I decided to fix the design such that it could have both bugs fixed. The original fix, fixed time reporting of the function graph tracer when doing a max_depth of one. This was code that can test how much the kernel interferes with userspace. But in doing so, it could corrupt the time keeping of the function profiler. The issue is that the curr_ret_stack variable was being used for two different meanings. One was to keep track of the stack pointer on the ret_stack (shadow stack used by the function graph tracer), and the other use case was the graph call depth. Although, the two may be closely related, where they got updated was the issue that lead to the two different bugs that required the two use cases to be updated differently. The big issue with this fix is that it requires changing each architecture. The good news is, I was able to remove a lot of code that was duplicated within the architectures and place it into a single location. Then I could make the fix in one place. I pushed this code into linux-next to let it settle over a week, and before doing so, I cross compiled all the affected architectures to make sure that they built fine. In the mean time, I also pulled in a patch that fixes the sched_switch previous tasks state output, that was not actually correct" * tag 'trace-v4.20-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: sched, trace: Fix prev_state output in sched_switch tracepoint function_graph: Have profiler use curr_ret_stack and not depth function_graph: Reverse the order of pushing the ret_stack and the callback function_graph: Move return callback before update of curr_ret_stack function_graph: Use new curr_ret_depth to manage depth instead of curr_ret_stack function_graph: Make ftrace_push_return_trace() static sparc/function_graph: Simplify with function_graph_enter() sh/function_graph: Simplify with function_graph_enter() s390/function_graph: Simplify with function_graph_enter() riscv/function_graph: Simplify with function_graph_enter() powerpc/function_graph: Simplify with function_graph_enter() parisc: function_graph: Simplify with function_graph_enter() nds32: function_graph: Simplify with function_graph_enter() MIPS: function_graph: Simplify with function_graph_enter() microblaze: function_graph: Simplify with function_graph_enter() arm64: function_graph: Simplify with function_graph_enter() ARM: function_graph: Simplify with function_graph_enter() x86/function_graph: Simplify with function_graph_enter() function_graph: Create function_graph_enter() to consolidate architecture code		2018-11-30 09:32:34 -08:00
..
boot	RISC-V: Build flat and compressed kernel images	2018-11-20 05:19:09 -08:00
configs	RISC-V: defconfig: Enable printk timestamps	2018-11-12 17:16:10 -08:00
include	riscv: add asm/unistd.h UAPI header	2018-11-20 05:19:20 -08:00
kernel	While rewriting the function graph tracer, I discovered a design flaw that	2018-11-30 09:32:34 -08:00
lib	RISC-V: lib: Fix build error for 64-bit	2018-11-12 18:09:55 -08:00
mm	mm: remove include/linux/bootmem.h	2018-10-31 08:54:16 -07:00
Kconfig	RISC-V Patches for the 4.20 Merge Window, Part 2 v2	2018-10-31 16:20:28 -07:00
Kconfig.debug	RISC-V: Cosmetic menuconfig changes	2018-10-22 17:38:20 -07:00
Makefile	RISC-V: Build flat and compressed kernel images	2018-11-20 05:19:09 -08:00