linux-kernel - [PATCH 3/3] arm64: ftrace: add cond_resched() to func ftrace_make

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Date:   Fri, 30 Nov 2018 16:09:56 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     rostedt@...dmis.org, mingo@...hat.com, catalin.marinas@....com,
        will.deacon@....com
Cc:     keescook@...omium.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Anders Roxell <anders.roxell@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 3/3] arm64: ftrace: add cond_resched() to func ftrace_make_(call|nop)

Both of those functions end up calling ftrace_modify_code(), which is
expensive because it changes the page tables and flush caches.
Microseconds add up because this is called in a loop for each dyn_ftrace
record, and this triggers the softlockup watchdog unless we let it sleep
occasionally.
Rework so that we call cond_resched() before going into the
ftrace_modify_code() function.

Co-developed-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
---
 arch/arm64/kernel/ftrace.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index de1a397d2d3f..9da38da58df7 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -130,6 +130,11 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	old = aarch64_insn_gen_nop();
 	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 
+	/* This function can take a long time when sanitizers are enabled, so
+	 * lets make sure we allow RCU processing.
+	 */
+	cond_resched();
+
 	return ftrace_modify_code(pc, old, new, true);
 }
 
@@ -188,6 +193,11 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 
 	new = aarch64_insn_gen_nop();
 
+	/* This function can take a long time when sanitizers are enabled, so
+	 * lets make sure we allow RCU processing.
+	 */
+	cond_resched();
+
 	return ftrace_modify_code(pc, old, new, validate);
 }
 
-- 
2.19.2