powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths

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_enabled',
which is checked on ftrace entry before continuing. This field can then
be set to zero to disable/pause ftrace, and set to a non-zero value to
resume ftrace.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 4185f1c9612501b51ffdafc2c8f125d1fa6ee1f3..163f13f31255c8e28273357d88e0b09d4fdf8632 100644 (file)
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -223,6 +223,7 @@ struct paca_struct {
        u8 hmi_event_available;         /* HMI event is available */
        u8 hmi_p9_special_emu;          /* HMI P9 special emulation */
 #endif
+       u8 ftrace_enabled;              /* Hard disable ftrace */
 
        /* Stuff for accurate time accounting */
        struct cpu_accounting_data accounting;

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 6bee65f3cfd34bf896ef770f805ec62d417ae9db..262c44a90ea1f68649c11fc87819a039669bce9e 100644 (file)
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -180,6 +180,7 @@ int main(void)
        OFFSET(PACAKMSR, paca_struct, kernel_msr);
        OFFSET(PACAIRQSOFTMASK, paca_struct, irq_soft_mask);
        OFFSET(PACAIRQHAPPENED, paca_struct, irq_happened);
+       OFFSET(PACA_FTRACE_ENABLED, paca_struct, ftrace_enabled);
 #ifdef CONFIG_PPC_BOOK3S
        OFFSET(PACACONTEXTID, paca_struct, mm_ctx_id);
 #ifdef CONFIG_PPC_MM_SLICES

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index b78f142a41488e1a91833112d5f3d1fe0c3bb4d0..313136006d1c3f2db7634381dd5537c687aca409 100644 (file)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -252,6 +252,9 @@ static void cpu_ready_for_interrupts(void)
 
        /* Set IR and DR in PACA MSR */
        get_paca()->kernel_msr = MSR_KERNEL;
+
+       /* We are now ok to enable ftrace */
+       get_paca()->ftrace_enabled = 1;
 }
 
 unsigned long spr_default_dscr = 0;

diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index 3f3e818524227f9bc7612b56b75d1c5efd32f5da..ae1cbe783ab6be9597810eb47a20479b1086494e 100644 (file)
--- 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_ENABLED(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 f095358da96e01f03ca33965b9aefe4bbd85a6c9..b7ba51a0f3b60b0ba91682d3a1f990aefbc5eafe 100644 (file)
--- 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_ENABLED(r13)
+       cmpdi   r3, 0
+       beqlr
+
        /* Taken from output of objdump from lib64/glibc */
        mflr    r3
        ld      r11, 0(r1)