| Message ID | b6aff6c7194bd7bb97828db63ca0c82ee4598918.1521627906.git.naveen.n.rao@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | powerpc/ftrace: Add support for ftrace_modify_call() and a few other fixes | expand |
On Wed, 21 Mar 2018 16:13:18 +0530 "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote: > We have some C code that we call into from real mode where we cannot > take any exceptions. Though the C functions themselves are mostly safe, > if these functions are traced, there is a possibility that we may take > an exception. For instance, in certain conditions, the ftrace code uses > WARN(), which uses a 'trap' to do its job. > > For such scenarios, introduce a new field in paca 'ftrace_disabled', > which is checked on ftrace entry before continuing. This field can then > be set to a non-zero value to disable/pause ftrace, and reset to zero to > resume ftrace. Looks fine to me: Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> -- Steve > > Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> > ---
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h index d2bf71dddbef..4f47adc2a408 100644 --- a/arch/powerpc/include/asm/paca.h +++ b/arch/powerpc/include/asm/paca.h @@ -211,6 +211,7 @@ struct paca_struct { u16 in_mce; u8 hmi_event_available; /* HMI event is available */ u8 hmi_p9_special_emu; /* HMI P9 special emulation */ + u8 ftrace_disabled; #endif /* Stuff for accurate time accounting */ diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index ea5eb91b836e..8e4fc96ff6bc 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -240,6 +240,7 @@ int main(void) OFFSET(PACA_RFI_FLUSH_FALLBACK_AREA, paca_struct, rfi_flush_fallback_area); OFFSET(PACA_EXRFI, paca_struct, exrfi); OFFSET(PACA_L1D_FLUSH_SIZE, paca_struct, l1d_flush_size); + OFFSET(PACA_FTRACE_DISABLED, paca_struct, ftrace_disabled); #endif OFFSET(PACAHWCPUID, paca_struct, hw_cpu_id); diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S index 3f3e81852422..8f2380304ef1 100644 --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S @@ -47,6 +47,12 @@ _GLOBAL(ftrace_caller) /* Save all gprs to pt_regs */ SAVE_GPR(0, r1) SAVE_10GPRS(2, r1) + + /* Ok to continue? */ + lbz r3, PACA_FTRACE_DISABLED(r13) + cmpdi r3, 0 + beq ftrace_no_trace + SAVE_10GPRS(12, r1) SAVE_10GPRS(22, r1) @@ -168,6 +174,14 @@ _GLOBAL(ftrace_graph_stub) _GLOBAL(ftrace_stub) blr +ftrace_no_trace: + mflr r3 + mtctr r3 + REST_GPR(3, r1) + addi r1, r1, SWITCH_FRAME_SIZE + mtlr r0 + bctr + #ifdef CONFIG_LIVEPATCH /* * This function runs in the mcount context, between two functions. As diff --git a/arch/powerpc/kernel/trace/ftrace_64_pg.S b/arch/powerpc/kernel/trace/ftrace_64_pg.S index f095358da96e..3d8186832a34 100644 --- a/arch/powerpc/kernel/trace/ftrace_64_pg.S +++ b/arch/powerpc/kernel/trace/ftrace_64_pg.S @@ -16,6 +16,10 @@ #ifdef CONFIG_DYNAMIC_FTRACE _GLOBAL_TOC(ftrace_caller) + lbz r3, PACA_FTRACE_DISABLED(r13) + cmpdi r3, 0 + bnelr + /* Taken from output of objdump from lib64/glibc */ mflr r3 ld r11, 0(r1)
We have some C code that we call into from real mode where we cannot take any exceptions. Though the C functions themselves are mostly safe, if these functions are traced, there is a possibility that we may take an exception. For instance, in certain conditions, the ftrace code uses WARN(), which uses a 'trap' to do its job. For such scenarios, introduce a new field in paca 'ftrace_disabled', which is checked on ftrace entry before continuing. This field can then be set to a non-zero value to disable/pause ftrace, and reset to zero to resume ftrace. Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> --- Changes since v1: - Do not guard the paca field check within CONFIG_KVM. - Move the early return code out of the usual path to optimize for better cache performance in the normal case when ftrace is enabled. arch/powerpc/include/asm/paca.h | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 14 ++++++++++++++ arch/powerpc/kernel/trace/ftrace_64_pg.S | 4 ++++ 4 files changed, 20 insertions(+)