Re: [PATCH v2 2/4] cpus: Make {start,end}_exclusive() recursive

[Richard Henderson]

On 2/13/23 02:52, Ilya Leoshkevich wrote:

Currently dying to one of the core_dump_signal()s deadlocks, because
dump_core_and_abort() calls start_exclusive() two times: first via
stop_all_tasks(), and then via preexit_cleanup() ->
qemu_plugin_user_exit().

There are a number of ways to solve this: resume after dumping core;
check cpu_in_exclusive_context() in qemu_plugin_user_exit(); or make
{start,end}_exclusive() recursive. Pick the last option, since it's
the most straightforward one.

Fixes: da91c1920242 ("linux-user: Clean up when exiting due to a signal")
Signed-off-by: Ilya Leoshkevich <i...@linux.ibm.com>
---
  cpus-common.c         | 12 ++++++++++--
  include/hw/core/cpu.h |  4 ++--
  2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/cpus-common.c b/cpus-common.c
index 793364dc0ed..a0c52cd187f 100644
--- a/cpus-common.c
+++ b/cpus-common.c
@@ -192,6 +192,11 @@ void start_exclusive(void)
      CPUState *other_cpu;
      int running_cpus;

+ if (current_cpu->exclusive_context_count) {

+        current_cpu->exclusive_context_count++;
+        return;
+    }
+
      qemu_mutex_lock(&qemu_cpu_list_lock);
      exclusive_idle();

@@ -219,13 +224,16 @@ void start_exclusive(void)

       */
      qemu_mutex_unlock(&qemu_cpu_list_lock);

- current_cpu->in_exclusive_context = true;

+    current_cpu->exclusive_context_count++;

I think this line would be clearer as "= 1".

Otherwise,
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>


r~