Re: [PATCH] replay: don't wait in run_on_cpu

[Pavel Dovgalyuk]

ping

On 11.03.2021 10:14, Pavel Dovgalyuk wrote:
> In record/replay mode waiting for vCPU to execute
> the task scheduled by run_on_cpu may lead to deadlock,
> because when run_on_cpu is executed in main_loop
> (e.g., in loadvm processing) it holds replay mutex.
> This patch allows running scheduled task in iothread
> when it holds the replay mutex.
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> ---
>   cpus-common.c            |    9 ++++++++-
>   include/sysemu/replay.h  |    1 +
>   replay/replay-internal.h |    1 -
>   stubs/replay-tools.c     |    5 +++++
>   4 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/cpus-common.c b/cpus-common.c
> index 6e73d3e58d..38ff510175 100644
> --- a/cpus-common.c
> +++ b/cpus-common.c
> @@ -23,6 +23,7 @@
>   #include "hw/core/cpu.h"
>   #include "sysemu/cpus.h"
>   #include "qemu/lockable.h"
> +#include "sysemu/replay.h"
>   
>   static QemuMutex qemu_cpu_list_lock;
>   static QemuCond exclusive_cond;
> @@ -136,7 +137,13 @@ void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, 
> run_on_cpu_data data,
>   {
>       struct qemu_work_item wi;
>   
> -    if (qemu_cpu_is_self(cpu)) {
> +    if (qemu_cpu_is_self(cpu)
> +        /*
> +         * vCPU thread is waiting when replay mutex is locked
> +         * and the task is not exclusive, the function may be called
> +         * without other synchronization.
> +         */
> +        || (replay_mode != REPLAY_MODE_NONE && replay_mutex_locked())) {
>           func(cpu, data);
>           return;
>       }
> diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
> index 0f3b0f7eac..032256533b 100644
> --- a/include/sysemu/replay.h
> +++ b/include/sysemu/replay.h
> @@ -62,6 +62,7 @@ extern char *replay_snapshot;
>   
>   void replay_mutex_lock(void);
>   void replay_mutex_unlock(void);
> +bool replay_mutex_locked(void);
>   
>   /* Replay process control functions */
>   
> diff --git a/replay/replay-internal.h b/replay/replay-internal.h
> index 97649ed8d7..dada623527 100644
> --- a/replay/replay-internal.h
> +++ b/replay/replay-internal.h
> @@ -117,7 +117,6 @@ void replay_get_array_alloc(uint8_t **buf, size_t *size);
>    * synchronisation between vCPU and main-loop threads. */
>   
>   void replay_mutex_init(void);
> -bool replay_mutex_locked(void);
>   
>   /*! Checks error status of the file. */
>   void replay_check_error(void);
> diff --git a/stubs/replay-tools.c b/stubs/replay-tools.c
> index 43296b3d4e..a42f2483d5 100644
> --- a/stubs/replay-tools.c
> +++ b/stubs/replay-tools.c
> @@ -48,6 +48,11 @@ void replay_mutex_unlock(void)
>   {
>   }
>   
> +bool replay_mutex_locked(void)
> +{
> +    return false;
> +}
> +
>   void replay_register_char_driver(Chardev *chr)
>   {
>   }