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Re: [Qemu-devel] [PATCH] cpus.c: qemu_mutex_lock_iothread fix race condi
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] cpus.c: qemu_mutex_lock_iothread fix race condition at cpu thread init |
Date: |
Fri, 4 Sep 2015 10:15:10 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
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 <address@hidden>
Cc: address@hidden
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 {
>