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Subject[PATCH 4.4 021/131] arm64: mm: Add trace_irqflags annotations to do_debug_exception()
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: James Morse <james.morse@arm.com>

commit 6afedcd23cfd7ac56c011069e4a8db37b46e4623 upstream.

With CONFIG_PROVE_LOCKING, CONFIG_DEBUG_LOCKDEP and CONFIG_TRACE_IRQFLAGS
enabled, lockdep will compare current->hardirqs_enabled with the flags from
local_irq_save().

When a debug exception occurs, interrupts are disabled in entry.S, but
lockdep isn't told, resulting in:
DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)
------------[ cut here ]------------
WARNING: at ../kernel/locking/lockdep.c:3523
Modules linked in:
CPU: 3 PID: 1752 Comm: perf Not tainted 4.5.0-rc4+ #2204
Hardware name: ARM Juno development board (r1) (DT)
task: ffffffc974868000 ti: ffffffc975f40000 task.ti: ffffffc975f40000
PC is at check_flags.part.35+0x17c/0x184
LR is at check_flags.part.35+0x17c/0x184
pc : [<ffffff80080fc93c>] lr : [<ffffff80080fc93c>] pstate: 600003c5
[...]
---[ end trace 74631f9305ef5020 ]---
Call trace:
[<ffffff80080fc93c>] check_flags.part.35+0x17c/0x184
[<ffffff80080ffe30>] lock_acquire+0xa8/0xc4
[<ffffff8008093038>] breakpoint_handler+0x118/0x288
[<ffffff8008082434>] do_debug_exception+0x3c/0xa8
[<ffffff80080854b4>] el1_dbg+0x18/0x6c
[<ffffff80081e82f4>] do_filp_open+0x64/0xdc
[<ffffff80081d6e60>] do_sys_open+0x140/0x204
[<ffffff80081d6f58>] SyS_openat+0x10/0x18
[<ffffff8008085d30>] el0_svc_naked+0x24/0x28
possible reason: unannotated irqs-off.
irq event stamp: 65857
hardirqs last enabled at (65857): [<ffffff80081fb1c0>] lookup_mnt+0xf4/0x1b4
hardirqs last disabled at (65856): [<ffffff80081fb188>] lookup_mnt+0xbc/0x1b4
softirqs last enabled at (65790): [<ffffff80080bdca4>] __do_softirq+0x1f8/0x290
softirqs last disabled at (65757): [<ffffff80080be038>] irq_exit+0x9c/0xd0

This patch adds the annotations to do_debug_exception(), while trying not
to call trace_hardirqs_off() if el1_dbg() interrupted a task that already
had irqs disabled.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/mm/fault.c | 33 +++++++++++++++++++++++----------
1 file changed, 23 insertions(+), 10 deletions(-)

--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -595,20 +595,33 @@ asmlinkage int __exception do_debug_exce
{
const struct fault_info *inf = debug_fault_info + DBG_ESR_EVT(esr);
struct siginfo info;
+ int rv;

- if (!inf->fn(addr, esr, regs))
- return 1;
+ /*
+ * Tell lockdep we disabled irqs in entry.S. Do nothing if they were
+ * already disabled to preserve the last enabled/disabled addresses.
+ */
+ if (interrupts_enabled(regs))
+ trace_hardirqs_off();

- pr_alert("Unhandled debug exception: %s (0x%08x) at 0x%016lx\n",
- inf->name, esr, addr);
+ if (!inf->fn(addr, esr, regs)) {
+ rv = 1;
+ } else {
+ pr_alert("Unhandled debug exception: %s (0x%08x) at 0x%016lx\n",
+ inf->name, esr, addr);

- info.si_signo = inf->sig;
- info.si_errno = 0;
- info.si_code = inf->code;
- info.si_addr = (void __user *)addr;
- arm64_notify_die("", regs, &info, 0);
+ info.si_signo = inf->sig;
+ info.si_errno = 0;
+ info.si_code = inf->code;
+ info.si_addr = (void __user *)addr;
+ arm64_notify_die("", regs, &info, 0);
+ rv = 0;
+ }

- return 0;
+ if (interrupts_enabled(regs))
+ trace_hardirqs_on();
+
+ return rv;
}

#ifdef CONFIG_ARM64_PAN

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