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Message-Id: <1269285449-1424-4-git-send-email-jason.wessel@windriver.com>
Date: Mon, 22 Mar 2010 14:17:24 -0500
From: Jason Wessel <jason.wessel@...driver.com>
To: torvalds@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
Jason Wessel <jason.wessel@...driver.com>
Subject: [PATCH 3/8] kgdb: eliminate kgdb_wait(), all cpus enter the same way
This is a kgdb architectural change to have all the cpus (master or
slave) enter the same function.
A cpu that hits an exception (wants to be the master cpu) will call
kgdb_handle_exception() from the trap handler and then invoke a
kgdb_roundup_cpu() to synchronize the other cpus and bring them into
the kgdb_handle_exception() as well.
A slave cpu will enter kgdb_handle_exception() from the
kgdb_nmicallback() and set the exception state to note that the
processor is a slave.
Previously the salve cpu would have called kgdb_wait(). This change
allows the debug core to change cpus without resuming the system in
order to inspect arch specific cpu information.
Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
---
kernel/debug/debug_core.c | 158 +++++++++++++++++++++-----------------------
kernel/debug/debug_core.h | 7 ++
2 files changed, 82 insertions(+), 83 deletions(-)
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index ad3caaa..91286e8 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -215,49 +215,6 @@ void __weak kgdb_disable_hw_debug(struct pt_regs *regs)
}
/*
- * CPU debug state control:
- */
-
-#ifdef CONFIG_SMP
-static void kgdb_wait(struct pt_regs *regs)
-{
- unsigned long flags;
- int cpu;
-
- local_irq_save(flags);
- cpu = raw_smp_processor_id();
- kgdb_info[cpu].debuggerinfo = regs;
- kgdb_info[cpu].task = current;
- /*
- * Make sure the above info reaches the primary CPU before
- * our cpu_in_kgdb[] flag setting does:
- */
- smp_wmb();
- atomic_set(&cpu_in_kgdb[cpu], 1);
-
- /* Disable any cpu specific hw breakpoints */
- kgdb_disable_hw_debug(regs);
-
- /* Wait till primary CPU is done with debugging */
- while (atomic_read(&passive_cpu_wait[cpu]))
- cpu_relax();
-
- kgdb_info[cpu].debuggerinfo = NULL;
- kgdb_info[cpu].task = NULL;
-
- /* fix up hardware debug registers on local cpu */
- if (arch_kgdb_ops.correct_hw_break)
- arch_kgdb_ops.correct_hw_break();
-
- /* Signal the primary CPU that we are done: */
- atomic_set(&cpu_in_kgdb[cpu], 0);
- touch_softlockup_watchdog_sync();
- clocksource_touch_watchdog();
- local_irq_restore(flags);
-}
-#endif
-
-/*
* Some architectures need cache flushes when we set/clear a
* breakpoint:
*/
@@ -486,34 +443,12 @@ static int kgdb_reenter_check(struct kgdb_state *ks)
return 1;
}
-/*
- * kgdb_handle_exception() - main entry point from a kernel exception
- *
- * Locking hierarchy:
- * interface locks, if any (begin_session)
- * kgdb lock (kgdb_active)
- */
-int
-kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
+static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs)
{
- struct kgdb_state kgdb_var;
- struct kgdb_state *ks = &kgdb_var;
unsigned long flags;
int sstep_tries = 100;
int error = 0;
int i, cpu;
-
- ks->cpu = raw_smp_processor_id();
- ks->ex_vector = evector;
- ks->signo = signo;
- ks->ex_vector = evector;
- ks->err_code = ecode;
- ks->kgdb_usethreadid = 0;
- ks->linux_regs = regs;
-
- if (kgdb_reenter_check(ks))
- return 0; /* Ouch, double exception ! */
-
acquirelock:
/*
* Interrupts will be restored by the 'trap return' code, except when
@@ -521,13 +456,42 @@ acquirelock:
*/
local_irq_save(flags);
- cpu = raw_smp_processor_id();
+ cpu = ks->cpu;
+ kgdb_info[cpu].debuggerinfo = regs;
+ kgdb_info[cpu].task = current;
+ /*
+ * Make sure the above info reaches the primary CPU before
+ * our cpu_in_kgdb[] flag setting does:
+ */
+ smp_wmb();
+ atomic_set(&cpu_in_kgdb[cpu], 1);
/*
- * Acquire the kgdb_active lock:
+ * CPU will loop if it is a slave or request to become a kgdb
+ * master cpu and acquire the kgdb_active lock:
*/
- while (atomic_cmpxchg(&kgdb_active, -1, cpu) != -1)
+ while (1) {
+ if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
+ if (atomic_cmpxchg(&kgdb_active, -1, cpu) == cpu)
+ break;
+ } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
+ if (!atomic_read(&passive_cpu_wait[cpu]))
+ goto return_normal;
+ } else {
+return_normal:
+ /* Return to normal operation by executing any
+ * hw breakpoint fixup.
+ */
+ if (arch_kgdb_ops.correct_hw_break)
+ arch_kgdb_ops.correct_hw_break();
+ atomic_set(&cpu_in_kgdb[cpu], 0);
+ touch_softlockup_watchdog_sync();
+ clocksource_touch_watchdog();
+ local_irq_restore(flags);
+ return 0;
+ }
cpu_relax();
+ }
/*
* For single stepping, try to only enter on the processor
@@ -561,9 +525,6 @@ acquirelock:
if (dbg_io_ops->pre_exception)
dbg_io_ops->pre_exception();
- kgdb_info[ks->cpu].debuggerinfo = ks->linux_regs;
- kgdb_info[ks->cpu].task = current;
-
kgdb_disable_hw_debug(ks->linux_regs);
/*
@@ -575,12 +536,6 @@ acquirelock:
atomic_set(&passive_cpu_wait[i], 1);
}
- /*
- * spin_lock code is good enough as a barrier so we don't
- * need one here:
- */
- atomic_set(&cpu_in_kgdb[ks->cpu], 1);
-
#ifdef CONFIG_SMP
/* Signal the other CPUs to enter kgdb_wait() */
if ((!kgdb_single_step) && kgdb_do_roundup)
@@ -612,8 +567,6 @@ acquirelock:
if (dbg_io_ops->post_exception)
dbg_io_ops->post_exception();
- kgdb_info[ks->cpu].debuggerinfo = NULL;
- kgdb_info[ks->cpu].task = NULL;
atomic_set(&cpu_in_kgdb[ks->cpu], 0);
if (!kgdb_single_step) {
@@ -646,13 +599,52 @@ kgdb_restore:
return error;
}
+/*
+ * kgdb_handle_exception() - main entry point from a kernel exception
+ *
+ * Locking hierarchy:
+ * interface locks, if any (begin_session)
+ * kgdb lock (kgdb_active)
+ */
+int
+kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
+{
+ struct kgdb_state kgdb_var;
+ struct kgdb_state *ks = &kgdb_var;
+ int ret;
+
+ ks->cpu = raw_smp_processor_id();
+ ks->ex_vector = evector;
+ ks->signo = signo;
+ ks->ex_vector = evector;
+ ks->err_code = ecode;
+ ks->kgdb_usethreadid = 0;
+ ks->linux_regs = regs;
+
+ if (kgdb_reenter_check(ks))
+ return 0; /* Ouch, double exception ! */
+ kgdb_info[ks->cpu].exception_state |= DCPU_WANT_MASTER;
+ ret = kgdb_cpu_enter(ks, regs);
+ kgdb_info[ks->cpu].exception_state &= ~DCPU_WANT_MASTER;
+ return ret;
+}
+
int kgdb_nmicallback(int cpu, void *regs)
{
#ifdef CONFIG_SMP
+ struct kgdb_state kgdb_var;
+ struct kgdb_state *ks = &kgdb_var;
+
+ memset(ks, 0, sizeof(struct kgdb_state));
+ ks->cpu = cpu;
+ ks->linux_regs = regs;
+
if (!atomic_read(&cpu_in_kgdb[cpu]) &&
- atomic_read(&kgdb_active) != cpu &&
- atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)])) {
- kgdb_wait((struct pt_regs *)regs);
+ atomic_read(&kgdb_active) != -1 &&
+ atomic_read(&kgdb_active) != cpu) {
+ kgdb_info[cpu].exception_state |= DCPU_IS_SLAVE;
+ kgdb_cpu_enter(ks, regs);
+ kgdb_info[cpu].exception_state &= ~DCPU_IS_SLAVE;
return 0;
}
#endif
diff --git a/kernel/debug/debug_core.h b/kernel/debug/debug_core.h
index 4b9d512..9825c5e 100644
--- a/kernel/debug/debug_core.h
+++ b/kernel/debug/debug_core.h
@@ -28,9 +28,16 @@ struct kgdb_state {
struct pt_regs *linux_regs;
};
+/* Exception state values */
+#define DCPU_WANT_MASTER 0x1 /* Waiting to become a master kgdb cpu */
+#define DCPU_NEXT_MASTER 0x2 /* Transition from one master cpu to another */
+#define DCPU_IS_SLAVE 0x4 /* Slave cpu enter exception */
+#define DCPU_SSTEP 0x8 /* CPU is single stepping */
+
struct debuggerinfo_struct {
void *debuggerinfo;
struct task_struct *task;
+ int exception_state;
};
extern struct debuggerinfo_struct kgdb_info[];
--
1.6.4.rc1
--
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