diff mbox series

[-next,V5,1/7] riscv: ftrace: Fixup panic by disabling preemption

Message ID 20221208091244.203407-2-guoren@kernel.org (mailing list archive)
State Superseded
Delegated to: Palmer Dabbelt
Headers show
Series riscv: Optimize function trace | expand

Checks

Context Check Description
conchuod/patch_count success Link
conchuod/cover_letter success Series has a cover letter
conchuod/tree_selection success Guessed tree name to be for-next
conchuod/fixes_present success Fixes tag not required for -next series
conchuod/verify_signedoff success Signed-off-by tag matches author and committer
conchuod/kdoc success Errors and warnings before: 0 this patch: 0
conchuod/module_param success Was 0 now: 0
conchuod/alphanumeric_selects success Out of order selects before the patch: 57 and now 57
conchuod/build_rv32_defconfig success Build OK
conchuod/build_warn_rv64 success Errors and warnings before: 0 this patch: 0
conchuod/dtb_warn_rv64 success Errors and warnings before: 0 this patch: 0
conchuod/header_inline success No static functions without inline keyword in header files
conchuod/checkpatch success total: 0 errors, 0 warnings, 0 checks, 8 lines checked
conchuod/source_inline success Was 0 now: 0
conchuod/build_rv64_nommu_k210_defconfig fail Build failed
conchuod/verify_fixes success Fixes tag looks correct
conchuod/build_rv64_nommu_virt_defconfig fail Build failed

Commit Message

Guo Ren Dec. 8, 2022, 9:12 a.m. UTC 
From: Andy Chiu <andy.chiu@sifive.com>

In RISCV, we must use an AUIPC + JALR pair to encode an immediate,
forming a jump that jumps to an address over 4K. This may cause errors
if we want to enable kernel preemption and remove dependency from
patching code with stop_machine(). For example, if a task was switched
out on auipc. And, if we changed the ftrace function before it was
switched back, then it would jump to an address that has updated 11:0
bits mixing with previous XLEN:12 part.

p: patched area performed by dynamic ftrace
ftrace_prologue:
p|      REG_S   ra, -SZREG(sp)
p|      auipc   ra, 0x? ------------> preempted
					...
				change ftrace function
					...
p|      jalr    -?(ra) <------------- switched back
p|      REG_L   ra, -SZREG(sp)
func:
	xxx
	ret

Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
@Andy, could you give the patch a Signed-off-by? I just copy your most
important comment, so the first author should be you. First, let's fix
the problem caused by my previous patch, and you can continue your
ftrace preemption work.
---
 arch/riscv/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index ef8d66de5f38..da59182cb5f1 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -136,7 +136,7 @@  config RISCV
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER
-	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
+	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
 
 config ARCH_MMAP_RND_BITS_MIN
 	default 18 if 64BIT