6.11-stable review patch. If anyone has any objections, please let me know.
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From: Vasily Gorbik gor@linux.ibm.com
commit a84dd0d8ae24bdc6da341187fc4c1a0adfce2ccc upstream.
ftrace_return_address() is called extremely often from performance-critical code paths when debugging features like CONFIG_TRACE_IRQFLAGS are enabled. For example, with debug_defconfig, ftrace selftests on my LPAR currently execute ftrace_return_address() as follows:
ftrace_return_address(0) - 0 times (common code uses __builtin_return_address(0) instead) ftrace_return_address(1) - 2,986,805,401 times (with this patch applied) ftrace_return_address(2) - 140 times ftrace_return_address(>2) - 0 times
The use of __builtin_return_address(n) was replaced by return_address() with an unwinder call by commit cae74ba8c295 ("s390/ftrace: Use unwinder instead of __builtin_return_address()") because __builtin_return_address(n) simply walks the stack backchain and doesn't check for reaching the stack top. For shallow stacks with fewer than "n" frames, this results in reads at low addresses and random memory accesses.
While calling the fully functional unwinder "works", it is very slow for this purpose. Moreover, potentially following stack switches and walking past IRQ context is simply wrong thing to do for ftrace_return_address().
Reimplement return_address() to essentially be __builtin_return_address(n) with checks for reaching the stack top. Since the ftrace_return_address(n) argument is always a constant, keep the implementation in the header, allowing both GCC and Clang to unroll the loop and optimize it to the bare minimum.
Fixes: cae74ba8c295 ("s390/ftrace: Use unwinder instead of __builtin_return_address()") Cc: stable@vger.kernel.org Reported-by: Sumanth Korikkar sumanthk@linux.ibm.com Reviewed-by: Heiko Carstens hca@linux.ibm.com Acked-by: Sumanth Korikkar sumanthk@linux.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/s390/include/asm/ftrace.h | 17 ++++++++++++++++- arch/s390/kernel/stacktrace.c | 19 ------------------- 2 files changed, 16 insertions(+), 20 deletions(-)
--- a/arch/s390/include/asm/ftrace.h +++ b/arch/s390/include/asm/ftrace.h @@ -6,8 +6,23 @@ #define MCOUNT_INSN_SIZE 6
#ifndef __ASSEMBLY__ +#include <asm/stacktrace.h>
-unsigned long return_address(unsigned int n); +static __always_inline unsigned long return_address(unsigned int n) +{ + struct stack_frame *sf; + + if (!n) + return (unsigned long)__builtin_return_address(0); + + sf = (struct stack_frame *)current_frame_address(); + do { + sf = (struct stack_frame *)sf->back_chain; + if (!sf) + return 0; + } while (--n); + return sf->gprs[8]; +} #define ftrace_return_address(n) return_address(n)
void ftrace_caller(void); --- a/arch/s390/kernel/stacktrace.c +++ b/arch/s390/kernel/stacktrace.c @@ -162,22 +162,3 @@ void arch_stack_walk_user(stack_trace_co { arch_stack_walk_user_common(consume_entry, cookie, NULL, regs, false); } - -unsigned long return_address(unsigned int n) -{ - struct unwind_state state; - unsigned long addr; - - /* Increment to skip current stack entry */ - n++; - - unwind_for_each_frame(&state, NULL, NULL, 0) { - addr = unwind_get_return_address(&state); - if (!addr) - break; - if (!n--) - return addr; - } - return 0; -} -EXPORT_SYMBOL_GPL(return_address);