[Qemu-devel] [PATCH] cpus.c: qemu_mutex_lock_iothread fix race condition at cpu thread init

[Qemu-devel] [PATCH] cpus.c: qemu_mutex_lock_iothread fix race condition at cpu thread init

[Aníbal Limón]

When QEMU starts the RCU thread executes qemu_mutex_lock_thread
causing error "qemu:qemu_cpu_kick_thread: No such process" and exits.

This isn't occur frequently but in glibc the thread id can exist and
this not guarantee that the thread is on active/running state. If is
inserted a sleep(1) after newthread assignment [1] the issue appears.

So not make assumption that thread exist if first_cpu->thread is set
then change the validation of cpu to created that is set into cpu
threads (kvm, tcg, dummy).

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_create.c;h=d10f4ea8004e1d8f3a268b95cc0f8d93b8d89867;hb=HEAD#l621

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
---
 cpus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cpus.c b/cpus.c
index 7e4786e..05e5400 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1171,7 +1171,7 @@ void qemu_mutex_lock_iothread(void)
      * TCG code execution.
      */
     if (!tcg_enabled() || qemu_in_vcpu_thread() ||
-        !first_cpu || !first_cpu->thread) {
+        !first_cpu || !first_cpu->created) {
         qemu_mutex_lock(&qemu_global_mutex);
         atomic_dec(&iothread_requesting_mutex);
     } else {
-- 
1.9.1

Re: [Qemu-devel] [PATCH] cpus.c: qemu_mutex_lock_iothread fix race condition at cpu thread init

[Paolo Bonzini]

On 03/09/2015 22:48, Aníbal Limón wrote:
> When QEMU starts the RCU thread executes qemu_mutex_lock_thread
> causing error "qemu:qemu_cpu_kick_thread: No such process" and exits.
> 
> This isn't occur frequently but in glibc the thread id can exist and
> this not guarantee that the thread is on active/running state. If is
> inserted a sleep(1) after newthread assignment [1] the issue appears.
> 
> So not make assumption that thread exist if first_cpu->thread is set
> then change the validation of cpu to created that is set into cpu
> threads (kvm, tcg, dummy).
> 
> [1] https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_create.c;h=d10f4ea8004e1d8f3a268b95cc0f8d93b8d89867;hb=HEAD#l621
> 
> Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>

Cc: qemu-stable@nongnu.org

Paolo

> ---
>  cpus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/cpus.c b/cpus.c
> index 7e4786e..05e5400 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -1171,7 +1171,7 @@ void qemu_mutex_lock_iothread(void)
>       * TCG code execution.
>       */
>      if (!tcg_enabled() || qemu_in_vcpu_thread() ||
> -        !first_cpu || !first_cpu->thread) {
> +        !first_cpu || !first_cpu->created) {
>          qemu_mutex_lock(&qemu_global_mutex);
>          atomic_dec(&iothread_requesting_mutex);
>      } else {
> 

[Qemu-devel] [PATCH] cpus.c: qemu_mutex_lock_iothread fix race condition at cpu thread init

[Aníbal Limón]

When QEMU starts the RCU thread executes qemu_mutex_lock_thread
causing error "qemu:qemu_cpu_kick_thread: No such process" and exits.

This isn't occur frequently but in glibc the thread id can exist and
this not guarantee that the thread is on active/running state. If is
inserted a sleep(1) after newthread assignment [1] the issue appears.

So not make assumption that thread exist if first_cpu->thread is set
then change the validation of cpu to created that is set into cpu
threads (kvm, tcg, dummy).

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_create.c;h=d10f4ea8004e1d8f3a268b95cc0f8d93b8d89867;hb=HEAD#l621

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
---
 cpus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cpus.c b/cpus.c
index 7e4786e..05e5400 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1171,7 +1171,7 @@ void qemu_mutex_lock_iothread(void)
      * TCG code execution.
      */
     if (!tcg_enabled() || qemu_in_vcpu_thread() ||
-        !first_cpu || !first_cpu->thread) {
+        !first_cpu || !first_cpu->created) {
         qemu_mutex_lock(&qemu_global_mutex);
         atomic_dec(&iothread_requesting_mutex);
     } else {
-- 
1.9.1