Ok, my first patch was pretty badly broken... try two.
Between the smp race on this test and set flag:
if (!KDB_STATE(PRINTF_LOCK)) {
KDB_STATE_SET(PRINTF_LOCK);
spin_lock(&kdb_printf_lock);
}
... and the fact that in the inner calls of a recursive kdb_printf this test
is trues:
if (KDB_STATE(PRINTF_LOCK)) {
spin_unlock(&kdb_printf_lock);
KDB_STATE_CLEAR(PRINTF_LOCK);
}
... the possibility exists to get the PRINTF_LOCK state and the spin_lock
state out of sync, eventually leading to a deadlock.
What I have done is intoduce a recursion count to ensure that only the outer
call is interacting with the smp serialization, with data locking to prevent
racing. This replaces the functionality of the KDB_STATE_PRINTF_LOCK.
--- /h/rsanders/trees/2.0_kdb4/ftl_future/linux/include/linux/kdb.h Tue
Jun 10 08:49:44 2003
+++ include/linux/kdb.h Tue Jun 10 11:01:10 2003
@@ -138,7 +138,7 @@
#define KDB_STATE_SUPPRESS 0x00000200 /* Suppress error messages
*/
#define KDB_STATE_LONGJMP 0x00000400 /* longjmp() data is
available */
#define KDB_STATE_GO_SWITCH 0x00000800 /* go is switching back to
initial cpu */
-#define KDB_STATE_PRINTF_LOCK 0x00001000 /* Holds kdb_printf lock */
+/* 0x00001000 Unused */
#define KDB_STATE_WAIT_IPI 0x00002000 /* Waiting for kdb_ipi() NMI
*/
#define KDB_STATE_RECURSE 0x00004000 /* Recursive entry to kdb */
#define KDB_STATE_IP_ADJUSTED 0x00008000 /* Restart IP has been
adjusted */
--- /h/rsanders/trees/2.0_kdb4/ftl_future/linux/kdb/kdb_io.c Tue Jun 10
08:49:44 2003
+++ kdb/kdb_io.c Tue Jun 10 11:04:33 2003
@@ -487,16 +487,20 @@
int logging, saved_loglevel = 0;
int do_longjmp = 0;
struct console *c = console_drivers;
- static spinlock_t kdb_printf_lock = SPIN_LOCK_UNLOCKED;
+ static spinlock_t data_lock = SPIN_LOCK_UNLOCKED;
+ static spinlock_t serialize_lock = SPIN_LOCK_UNLOCKED;
+ static int recursion_count[NR_CPUS] = { 0 };
/* Serialize kdb_printf if multiple cpus try to write at once.
* But if any cpu goes recursive in kdb, just print the output,
* even if it is interleaved with any other text.
*/
- if (!KDB_STATE(PRINTF_LOCK)) {
- KDB_STATE_SET(PRINTF_LOCK);
- spin_lock(&kdb_printf_lock);
- }
+ spin_lock(&data_lock);
+ /* attempt to grab the lock only on the root call of this recurse */
+ if ( !recursion_count[smp_processor_id()] )
+ spin_lock(&serialize_lock);
+ ++recursion_count[smp_processor_id()];
+ spin_unlock(&data_lock);
diag = kdbgetintenv("LINES", &linecount);
if (diag || linecount <= 1)
@@ -591,10 +595,17 @@
if (logging) {
console_loglevel = saved_loglevel;
}
- if (KDB_STATE(PRINTF_LOCK)) {
- spin_unlock(&kdb_printf_lock);
- KDB_STATE_CLEAR(PRINTF_LOCK);
- }
+
+ spin_lock(&data_lock);
+ --recursion_count[smp_processor_id()];
+ /*
+ * only clear the serialization lock if this is the root call
+ * and not one of the nested calls
+ */
+ if ( !recursion_count[smp_processor_id()] )
+ spin_unlock(&serialize_lock);
+ spin_unlock(&data_lock);
+
if (do_longjmp)
#ifdef KDB_HAVE_LONGJMP
kdba_longjmp(&kdbjmpbuf[smp_processor_id()], 1)
