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Subject[RFC PATCH 1/2] debug: Convert dbg_slave_lock to an atomic
Date
Currently the debug core takes and releases dbg_slave_lock, knowing it to
be uncontended, as a means to set and clear a flag that it uses to herd
the other cores in to or out of a holding pen.

Let's convert this to a regular atomic instead. This change is worthwhile
simply for the subtle increase in clarity in a very tangled bit of code.
It is also useful because it removes a raw_spin_lock() from within the
debug trap, which will make it easier to introduce spin lock debugging
code for the debug trap handler.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
kernel/debug/debug_core.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 2b7c9b67931d..8f43171ddeac 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -121,12 +121,12 @@ static struct kgdb_bkpt kgdb_break[KGDB_MAX_BREAKPOINTS] = {
atomic_t kgdb_active = ATOMIC_INIT(-1);
EXPORT_SYMBOL_GPL(kgdb_active);
static DEFINE_RAW_SPINLOCK(dbg_master_lock);
-static DEFINE_RAW_SPINLOCK(dbg_slave_lock);

/*
* We use NR_CPUs not PERCPU, in case kgdb is used to debug early
* bootup code (which might not have percpu set up yet):
*/
+static atomic_t slaves_must_spin;
static atomic_t masters_in_kgdb;
static atomic_t slaves_in_kgdb;
static atomic_t kgdb_break_tasklet_var;
@@ -615,7 +615,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
dump_stack();
kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
} else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
- if (!raw_spin_is_locked(&dbg_slave_lock))
+ if (!atomic_read(&slaves_must_spin))
goto return_normal;
} else {
return_normal:
@@ -677,7 +677,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
* CPU in a spin state while the debugger is active
*/
if (!kgdb_single_step)
- raw_spin_lock(&dbg_slave_lock);
+ atomic_set(&slaves_must_spin, 1);

#ifdef CONFIG_SMP
/* If send_ready set, slaves are already waiting */
@@ -741,7 +741,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
dbg_io_ops->post_exception();

if (!kgdb_single_step) {
- raw_spin_unlock(&dbg_slave_lock);
+ atomic_set(&slaves_must_spin, 0);
/* Wait till all the CPUs have quit from the debugger. */
while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
cpu_relax();
--
2.25.4
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