Re: [Qemu-devel] [PATCH v2 06/11] sparc/sparc64: grab BQL before calling cpu_check_irqs

[Paolo Bonzini]

On 06/03/2017 11:28, Alex Bennée wrote:
>> This can be called from gdbstub, so you need to put the lock/unlock
>> around helper_wrpsr's call to cpu_put_psr instead.  Also please add a
>> comment /* Called with BQL held.  */ around cpu_put_psr.
> 
> OK will do. I have to say its hard to see the gdbstub being under the
> BQL. Is this a feature of the packet handling being done in the main IO
> thread?

Yes.

It's probably nigh time to have stronger debug facilities for locks,
including changing our lock policy comments to optional assertions.

I'm even thinking of doing something like C++'s std::unique_lock, for
example

    // Takes a lock and unlocks it when the scope is left.
    // c++: std::lock_guard<std::mutex> sl(some_lock);
    QEMU_SCOPED_MUTEX(QemuMutex, some_lock) sl;


    // The lock is also unlocked correctly when the scope is left.
    // c++: std::unique_lock<std::mutex> sl(some_lock);
    QEMU_SCOPED_MUTEX(QemuMutex, some_lock) sl;
    ...
    for (;;) {
        qemu_scoped_mutex_unlock(&sl);
        if (foo) {
            break;
        }
        ...
        qemu_scoped_mutex_lock(&sl);
    }

    // The lock is taken later.
    // c++: std::unique_lock<std::mutex> sl(some_lock, std::defer_lock);
    QEMU_SCOPED_MUTEX_DEFER(QemuMutex, some_lock) sl;
    ...
    if (x) {
        qemu_scoped_mutex_lock(&sl);
    }

Paolo