[RFC PATCH v2 2/5] powerpc/ftrace: Remove pointer to struct module from dyn_arch_ftrace

[Naveen N Rao <naveen@kernel.org>]

Pointer to struct module is only relevant for ftrace records belonging
to kernel modules. Having this field in dyn_arch_ftrace wastes memory
for all ftrace records belonging to the kernel. Remove the same in
favour of looking up the module from the ftrace record address, similar
to other architectures.

Signed-off-by: Naveen N Rao <naveen@kernel.org>
---
 arch/powerpc/include/asm/ftrace.h        |  1 -
 arch/powerpc/kernel/trace/ftrace.c       | 47 ++++++++++-----
 arch/powerpc/kernel/trace/ftrace_64_pg.c | 73 +++++++++++-------------
 3 files changed, 64 insertions(+), 57 deletions(-)

diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 107fc5a48456..201f9d15430a 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -26,7 +26,6 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 struct module;
 struct dyn_ftrace;
 struct dyn_arch_ftrace {
-	struct module *mod;
 };
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index d8d6b4fd9a14..041be965485e 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -106,20 +106,36 @@ static unsigned long find_ftrace_tramp(unsigned long ip)
 	return 0;
 }
 
+static struct module *ftrace_lookup_module(struct dyn_ftrace *rec)
+{
+	struct module *mod = NULL;
+
+#ifdef CONFIG_MODULES
+	/*
+	 * NOTE: __module_text_address() must be called with preemption
+	 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
+	 * retains its validity throughout the remainder of this code.
+	*/
+	preempt_disable();
+	mod = __module_text_address(rec->ip);
+	preempt_enable();
+
+	if (!mod)
+		pr_err("No module loaded at addr=%lx\n", rec->ip);
+#endif
+
+	return mod;
+}
+
 static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_inst_t *call_inst)
 {
 	unsigned long ip = rec->ip;
 	unsigned long stub;
+	struct module *mod;
 
 	if (is_offset_in_branch_range(addr - ip)) {
 		/* Within range */
 		stub = addr;
-#ifdef CONFIG_MODULES
-	} else if (rec->arch.mod) {
-		/* Module code would be going to one of the module stubs */
-		stub = (addr == (unsigned long)ftrace_caller ? rec->arch.mod->arch.tramp :
-							       rec->arch.mod->arch.tramp_regs);
-#endif
 	} else if (core_kernel_text(ip)) {
 		/* We would be branching to one of our ftrace stubs */
 		stub = find_ftrace_tramp(ip);
@@ -128,7 +144,16 @@ static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_
 			return -EINVAL;
 		}
 	} else {
-		return -EINVAL;
+		mod = ftrace_lookup_module(rec);
+		if (mod) {
+#ifdef CONFIG_MODULES
+			/* Module code would be going to one of the module stubs */
+			stub = (addr == (unsigned long)ftrace_caller ? mod->arch.tramp :
+								       mod->arch.tramp_regs);
+#endif
+		} else {
+			return -EINVAL;
+		}
 	}
 
 	*call_inst = ftrace_create_branch_inst(ip, stub, 1);
@@ -256,14 +281,6 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	if (ret)
 		return ret;
 
-	if (!core_kernel_text(ip)) {
-		if (!mod) {
-			pr_err("0x%lx: No module provided for non-kernel address\n", ip);
-			return -EFAULT;
-		}
-		rec->arch.mod = mod;
-	}
-
 	/* Nop-out the ftrace location */
 	new = ppc_inst(PPC_RAW_NOP());
 	addr = MCOUNT_ADDR;
diff --git a/arch/powerpc/kernel/trace/ftrace_64_pg.c b/arch/powerpc/kernel/trace/ftrace_64_pg.c
index 12fab1803bcf..45bd8dcf9886 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_pg.c
+++ b/arch/powerpc/kernel/trace/ftrace_64_pg.c
@@ -116,6 +116,24 @@ static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op)
 }
 
 #ifdef CONFIG_MODULES
+static struct module *ftrace_lookup_module(struct dyn_ftrace *rec)
+{
+	struct module *mod;
+	/*
+	 * NOTE: __module_text_address() must be called with preemption
+	 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
+	 * retains its validity throughout the remainder of this code.
+	*/
+	preempt_disable();
+	mod = __module_text_address(rec->ip);
+	preempt_enable();
+
+	if (!mod)
+		pr_err("No module loaded at addr=%lx\n", rec->ip);
+
+	return mod;
+}
+
 static int
 __ftrace_make_nop(struct module *mod,
 		  struct dyn_ftrace *rec, unsigned long addr)
@@ -124,6 +142,12 @@ __ftrace_make_nop(struct module *mod,
 	unsigned long ip = rec->ip;
 	ppc_inst_t op, pop;
 
+	if (!mod) {
+		mod = ftrace_lookup_module(rec);
+		if (!mod)
+			return -EINVAL;
+	}
+
 	/* read where this goes */
 	if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {
 		pr_err("Fetching opcode failed.\n");
@@ -366,27 +390,6 @@ int ftrace_make_nop(struct module *mod,
 		return -EINVAL;
 	}
 
-	/*
-	 * Out of range jumps are called from modules.
-	 * We should either already have a pointer to the module
-	 * or it has been passed in.
-	 */
-	if (!rec->arch.mod) {
-		if (!mod) {
-			pr_err("No module loaded addr=%lx\n", addr);
-			return -EFAULT;
-		}
-		rec->arch.mod = mod;
-	} else if (mod) {
-		if (mod != rec->arch.mod) {
-			pr_err("Record mod %p not equal to passed in mod %p\n",
-			       rec->arch.mod, mod);
-			return -EINVAL;
-		}
-		/* nothing to do if mod == rec->arch.mod */
-	} else
-		mod = rec->arch.mod;
-
 	return __ftrace_make_nop(mod, rec, addr);
 }
 
@@ -411,7 +414,10 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	ppc_inst_t op[2];
 	void *ip = (void *)rec->ip;
 	unsigned long entry, ptr, tramp;
-	struct module *mod = rec->arch.mod;
+	struct module *mod = ftrace_lookup_module(rec);
+
+	if (!mod)
+		return -EINVAL;
 
 	/* read where this goes */
 	if (copy_inst_from_kernel_nofault(op, ip))
@@ -533,16 +539,6 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 		return -EINVAL;
 	}
 
-	/*
-	 * Out of range jumps are called from modules.
-	 * Being that we are converting from nop, it had better
-	 * already have a module defined.
-	 */
-	if (!rec->arch.mod) {
-		pr_err("No module loaded\n");
-		return -EINVAL;
-	}
-
 	return __ftrace_make_call(rec, addr);
 }
 
@@ -555,7 +551,10 @@ __ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 	ppc_inst_t op;
 	unsigned long ip = rec->ip;
 	unsigned long entry, ptr, tramp;
-	struct module *mod = rec->arch.mod;
+	struct module *mod = ftrace_lookup_module(rec);
+
+	if (!mod)
+		return -EINVAL;
 
 	/* If we never set up ftrace trampolines, then bail */
 	if (!mod->arch.tramp || !mod->arch.tramp_regs) {
@@ -668,14 +667,6 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 		return -EINVAL;
 	}
 
-	/*
-	 * Out of range jumps are called from modules.
-	 */
-	if (!rec->arch.mod) {
-		pr_err("No module loaded\n");
-		return -EINVAL;
-	}
-
 	return __ftrace_modify_call(rec, old_addr, addr);
 }
 #endif
-- 
2.45.2