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authorJason Wessel <jason.wessel@windriver.com>2008-04-01 16:55:27 -0500
committerIngo Molnar <mingo@elte.hu>2008-04-17 20:05:43 +0200
commit56fb70932964927597ce30bbd820471633c72adc (patch)
tree72654913a07cbc83f174234d4fa0f91b79a2164c /kernel/kgdb.c
parent225a4424ade24e913c081d5a4c4bd71a0fe2e0ac (diff)
downloadlinux-56fb70932964927597ce30bbd820471633c72adc.tar.bz2
kgdb: fix SMP NMI kgdb_handle_exception exit race
Fix the problem of protecting the kgdb handle_exception exit which had an NMI race condition, while trying to restore normal system operation. There was a small window after the master processor sets cpu_in_debug to zero but before it has set kgdb_active to zero where a non-master processor in an SMP system could receive an NMI and re-enter the kgdb_wait() loop. As long as the master processor sets the cpu_in_debug before sending the cpu roundup the cpu_in_debug variable can also be used to guard against the race condition. The kgdb_wait() function no longer needs to check kgdb_active because it is done in the arch specific code and handled along with the nmi traps at the low level. This also allows kgdb_wait() to exit correctly if it was entered for some unknown reason due to a spurious NMI that could not be handled by the arch specific code. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/kgdb.c')
-rw-r--r--kernel/kgdb.c27
1 files changed, 8 insertions, 19 deletions
diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 85b7e5b934a7..4d1b3c232377 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -561,18 +561,6 @@ static void kgdb_wait(struct pt_regs *regs)
smp_wmb();
atomic_set(&cpu_in_kgdb[cpu], 1);
- /*
- * The primary CPU must be active to enter here, but this is
- * guard in case the primary CPU had not been selected if
- * this was an entry via nmi.
- */
- while (atomic_read(&kgdb_active) == -1)
- cpu_relax();
-
- /* Wait till primary CPU goes completely into the debugger. */
- while (!atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)]))
- cpu_relax();
-
/* Wait till primary CPU is done with debugging */
while (atomic_read(&passive_cpu_wait[cpu]))
cpu_relax();
@@ -1447,18 +1435,18 @@ acquirelock:
atomic_set(&passive_cpu_wait[i], 1);
}
-#ifdef CONFIG_SMP
- /* Signal the other CPUs to enter kgdb_wait() */
- if ((!kgdb_single_step || !kgdb_contthread) && kgdb_do_roundup)
- kgdb_roundup_cpus(flags);
-#endif
-
/*
* 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_contthread) && kgdb_do_roundup)
+ kgdb_roundup_cpus(flags);
+#endif
+
/*
* Wait for the other CPUs to be notified and be waiting for us:
*/
@@ -1514,7 +1502,8 @@ int kgdb_nmicallback(int cpu, void *regs)
{
#ifdef CONFIG_SMP
if (!atomic_read(&cpu_in_kgdb[cpu]) &&
- atomic_read(&kgdb_active) != cpu) {
+ atomic_read(&kgdb_active) != cpu &&
+ atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)])) {
kgdb_wait((struct pt_regs *)regs);
return 0;
}