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authorJason Wessel <jason.wessel@windriver.com>2009-12-11 17:43:17 +0300
committerJason Wessel <jason.wessel@windriver.com>2009-12-11 17:43:17 +0300
commit028e7b175970be8fca58bfd7d61cc375babe40b7 (patch)
treec94d3acdc460836a9ef2d06f3e80f83d5f33f157 /kernel/kgdb.c
parentcf6f196d112a6f6757b1ca3cce0b576f7abee479 (diff)
downloadlinux-028e7b175970be8fca58bfd7d61cc375babe40b7.tar.xz
kgdb: allow for cpu switch when single stepping
The kgdb core should not assume that a single step operation of a kernel thread will complete on the same CPU. The single step flag is set at the "thread" level and it is possible in a multi cpu system that a kernel thread can get scheduled on another cpu the next time it is run. As a further safety net in case a slave cpu is hung, the debug master cpu will try 100 times before giving up and assuming control of the slave cpus is no longer possible. It is more useful to be able to get some information out of kgdb instead of spinning forever. Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Diffstat (limited to 'kernel/kgdb.c')
-rw-r--r--kernel/kgdb.c20
1 files changed, 15 insertions, 5 deletions
diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 29357a9ccfb2..ca21fe98e8de 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -129,6 +129,7 @@ struct task_struct *kgdb_usethread;
struct task_struct *kgdb_contthread;
int kgdb_single_step;
+pid_t kgdb_sstep_pid;
/* Our I/O buffers. */
static char remcom_in_buffer[BUFMAX];
@@ -1400,6 +1401,7 @@ kgdb_handle_exception(int evector, int signo, int ecode, 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;
@@ -1430,13 +1432,14 @@ acquirelock:
cpu_relax();
/*
- * Do not start the debugger connection on this CPU if the last
- * instance of the exception handler wanted to come into the
- * debugger on a different CPU via a single step
+ * For single stepping, try to only enter on the processor
+ * that was single stepping. To gaurd against a deadlock, the
+ * kernel will only try for the value of sstep_tries before
+ * giving up and continuing on.
*/
if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
- atomic_read(&kgdb_cpu_doing_single_step) != cpu) {
-
+ (kgdb_info[cpu].task &&
+ kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
atomic_set(&kgdb_active, -1);
touch_softlockup_watchdog();
clocksource_touch_watchdog();
@@ -1529,6 +1532,13 @@ acquirelock:
}
kgdb_restore:
+ if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
+ int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
+ if (kgdb_info[sstep_cpu].task)
+ kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
+ else
+ kgdb_sstep_pid = 0;
+ }
/* Free kgdb_active */
atomic_set(&kgdb_active, -1);
touch_softlockup_watchdog();