arm64: Add user_debug command line option

Commit Message

Laura Abbott April 9, 2014, 1:45 a.m. UTC

arm had a useful command line option to print out debug
information on user signals. This is somewhat like a more verbose
version of show_unhandled_signals. Add the user_debug command line
option to print out more information in a similar manner to
arm.

Signed-off-by: Laura Abbott <[e-mail]>
---
 arch/arm64/include/asm/system_misc.h | 25 +++++++++++++++++++++++++
 arch/arm64/kernel/traps.c            | 13 ++++++++++---
 arch/arm64/mm/fault.c                |  3 +--
 3 files changed, 36 insertions(+), 5 deletions(-)

Comments

Catalin Marinas April 9, 2014, 8:41 a.m. UTC | #1

On Wed, Apr 09, 2014 at 02:45:08AM +0100, Laura Abbott wrote:
> arm had a useful command line option to print out debug
> information on user signals. This is somewhat like a more verbose
> version of show_unhandled_signals. Add the user_debug command line
> option to print out more information in a similar manner to
> arm.

Is this because you want to print information for handled signals as
well? What is the use case? (there are alternatives like ptrace as
well).

Laura Abbott April 9, 2014, 6:11 p.m. UTC | #2

On 4/9/2014 1:41 AM, Catalin Marinas wrote:
> On Wed, Apr 09, 2014 at 02:45:08AM +0100, Laura Abbott wrote:
>> arm had a useful command line option to print out debug
>> information on user signals. This is somewhat like a more verbose
>> version of show_unhandled_signals. Add the user_debug command line
>> option to print out more information in a similar manner to
>> arm.
> 
> Is this because you want to print information for handled signals as
> well? What is the use case? (there are alternatives like ptrace as
> well).
> 

Yes. We've found user_debug to be helpful in correlating userspace
crashes to other events that are spewed in the system log. Example
from last week: userspace program crashes, bad page state and panic
happens soon after. Some kernel driver was not cleaning up after
itself properly after the crash. Without seeing the userspace crash
logs it would have been much more difficult to correlate the bad
page state to anything.

Laura

Patch

diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h
index 7a18fab..2f95589 100644
--- a/arch/arm64/include/asm/system_misc.h
+++ b/arch/arm64/include/asm/system_misc.h
@@ -50,6 +50,31 @@  extern void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
 #define UDBG_SEGV	(1 << 3)
 #define UDBG_BUS	(1 << 4)
 
+extern unsigned int user_debug;
+extern int show_unhandled_signals;
+
+static inline bool print_user_debug(unsigned int signum, unsigned int mask)
+{
+	int ret = 0;
+	bool sig_assert = false;
+
+	ret |= show_unhandled_signals &&
+		(signum ? unhandled_signal(current, signum) : 1);
+	if (mask & UDBG_SEGV) {
+		sig_assert = true;
+		ret |= (user_debug & mask) && signum == SIGSEGV;
+	}
+	if (mask & UDBG_BUS) {
+		sig_assert = true;
+		ret |= (user_debug & mask) && signum == SIGBUS;
+	}
+	if (sig_assert)
+		ret |= (user_debug & mask);
+
+	return ret ? printk_ratelimit() : false;
+}
+
+
 #endif	/* __ASSEMBLY__ */
 
 #endif	/* __ASM_SYSTEM_MISC_H */
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index a6740d0..5519ef1 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -48,6 +48,14 @@  static const char *handler[]= {
 };
 
 int show_unhandled_signals = 1;
+unsigned int user_debug;
+
+static int __init user_debug_setup(char *str)
+{
+	get_option(&str, &user_debug);
+	return 1;
+}
+__setup("user_debug=", user_debug_setup);
 
 /*
  * Dump out the contents of some memory nicely...
@@ -270,8 +278,7 @@  asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
 
 	trace_undef_instr(regs, (void *)pc);
 
-	if (show_unhandled_signals && unhandled_signal(current, SIGILL) &&
-	    printk_ratelimit()) {
+	if (print_user_debug(SIGILL, UDBG_UNDEFINED)) {
 		pr_info("%s[%d]: undefined instruction: pc=%p\n",
 			current->comm, task_pid_nr(current), pc);
 		dump_instr(KERN_INFO, regs);
@@ -298,7 +305,7 @@  asmlinkage long do_ni_syscall(struct pt_regs *regs)
 	}
 #endif
 
-	if (show_unhandled_signals && printk_ratelimit()) {
+	if (print_user_debug(0, UDBG_SYSCALL)) {
 		pr_info("%s[%d]: syscall %d\n", current->comm,
 			task_pid_nr(current), (int)regs->syscallno);
 		dump_instr("", regs);
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 8e783eb..bbef0b5 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -117,8 +117,7 @@  static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 
 	trace_user_fault(tsk, addr, esr);
 
-	if (show_unhandled_signals && unhandled_signal(tsk, sig) &&
-	    printk_ratelimit()) {
+	if (print_user_debug(sig, UDBG_BUS | UDBG_SEGV)) {
 		pr_info("%s[%d]: unhandled %s (%d) at 0x%08lx, esr 0x%03x\n",
 			tsk->comm, task_pid_nr(tsk), fault_name(esr), sig,
 			addr, esr);