[PATCH] kvm tools: Fix 'kill -3' hangs

[Pekka Enberg <penberg@kernel.org>]

Ingo Molnar reported that 'kill -3' didn't work on his machine:

  * Ingo Molnar <mingo@elte.hu> wrote:

  > This is really cumbersome to debug - is there some good way to get to the RIP
  > that the guest is hanging in? If kvm would print that out to the host console
  > (even if it's just the raw RIP initially) on a kill -3 that would help
  > enormously.

  Looks like the code should be doing that already - but the ioctl(KVM_GET_SREGS)
  hangs:

    [pid   748] ioctl(6, KVM_GET_SREGS

Avi Kivity pointed out that it's not safe to call KVM_GET_SREGS (or other vcpu
related ioctls) from other threads:

  > is it not OK to call KVM_GET_SREGS from other threads than the one
  > that's doing KVM_RUN?

  From Documentation/kvm/api.txt:

   - vcpu ioctls: These query and set attributes that control the operation
     of a single virtual cpu.

     Only run vcpu ioctls from the same thread that was used to create the
     vcpu.

Fix that up by using pthread_kill() to force the threads that are doing KVM_RUN
to do the register dumps.

Reported: Ingo Molnar <mingo@elte.hu>
Cc: Asias He <asias.hejun@gmail.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
 tools/kvm/kvm-run.c |   20 +++++++++++++++++---
 1 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index eb50b6a..58e2977 100644
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -127,6 +127,18 @@ static const struct option options[] = {
 	OPT_END()
 };
 
+static void handle_sigusr1(int sig)
+{
+	struct kvm_cpu *cpu = current_kvm_cpu;
+
+	if (!cpu)
+		return;
+
+	kvm_cpu__show_registers(cpu);
+	kvm_cpu__show_code(cpu);
+	kvm_cpu__show_page_tables(cpu);
+}
+
 static void handle_sigquit(int sig)
 {
 	int i;
@@ -134,9 +146,10 @@ static void handle_sigquit(int sig)
 	for (i = 0; i < nrcpus; i++) {
 		struct kvm_cpu *cpu = kvm_cpus[i];
 
-		kvm_cpu__show_registers(cpu);
-		kvm_cpu__show_code(cpu);
-		kvm_cpu__show_page_tables(cpu);
+		if (!cpu)
+			continue;
+
+		pthread_kill(cpu->thread, SIGUSR1);
 	}
 
 	serial8250__inject_sysrq(kvm);
@@ -332,6 +345,7 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 
 	signal(SIGALRM, handle_sigalrm);
 	signal(SIGQUIT, handle_sigquit);
+	signal(SIGUSR1, handle_sigusr1);
 
 	while (argc != 0) {
 		argc = parse_options(argc, argv, options, run_usage,
-- 
1.7.0.4