From f0cbb49e2a44bcf5a515922b96853acc1bed3b79 Mon Sep 17 00:00:00 2001 From: Emanuele Giuseppe Esposito Date: Thu, 3 Mar 2022 10:15:46 -0500 Subject: [PATCH 7/8] main-loop.h: introduce qemu_in_main_thread() When invoked from the main loop, this function is the same as qemu_mutex_iothread_locked, and returns true if the BQL is held. When invoked from iothreads or tests, it returns true only if the current AioContext is the Main Loop. This essentially just extends qemu_mutex_iothread_locked to work also in unit tests or other users like storage-daemon, that run in the Main Loop but end up using the implementation in stubs/iothread-lock.c. Using qemu_mutex_iothread_locked in unit tests defaults to false because they use the implementation in stubs/iothread-lock, making all assertions added in next patches fail despite the AioContext is still the main loop. See the comment in the function header for more information. Signed-off-by: Emanuele Giuseppe Esposito Message-Id: <20220303151616.325444-2-eesposit@redhat.com> Signed-off-by: Kevin Wolf --- cpus.c | 5 +++++ include/qemu/main-loop.h | 24 ++++++++++++++++++++++++ stubs/Makefile.objs | 1 + stubs/iothread-lock-block.c | 8 ++++++++ 4 files changed, 38 insertions(+) create mode 100644 stubs/iothread-lock-block.c diff --git a/cpus.c b/cpus.c index b2a26a1f11..d2d486129d 100644 --- a/cpus.c +++ b/cpus.c @@ -1848,6 +1848,11 @@ bool qemu_mutex_iothread_locked(void) return iothread_locked; } +bool qemu_in_main_thread(void) +{ + return qemu_mutex_iothread_locked(); +} + /* * The BQL is taken from so many places that it is worth profiling the * callers directly, instead of funneling them all through a single function. diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h index cba048bc82..42d65cf270 100644 --- a/include/qemu/main-loop.h +++ b/include/qemu/main-loop.h @@ -260,9 +260,33 @@ int qemu_add_child_watch(pid_t pid); * must always be taken outside other locks. This function helps * functions take different paths depending on whether the current * thread is running within the main loop mutex. + * + * This function should never be used in the block layer, because + * unit tests, block layer tools and qemu-storage-daemon do not + * have a BQL. + * Please instead refer to qemu_in_main_thread(). */ bool qemu_mutex_iothread_locked(void); +/** + * qemu_in_main_thread: return whether it's possible to safely access + * the global state of the block layer. + * + * Global state of the block layer is not accessible from I/O threads + * or worker threads; only from threads that "own" the default + * AioContext that qemu_get_aio_context() returns. For tests, block + * layer tools and qemu-storage-daemon there is a designated thread that + * runs the event loop for qemu_get_aio_context(), and that is the + * main thread. + * + * For emulators, however, any thread that holds the BQL can act + * as the block layer main thread; this will be any of the actual + * main thread, the vCPU threads or the RCU thread. + * + * For clarity, do not use this function outside the block layer. + */ +bool qemu_in_main_thread(void); + /** * qemu_mutex_lock_iothread: Lock the main loop mutex. * diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs index 9c7393b08c..e748ccd323 100644 --- a/stubs/Makefile.objs +++ b/stubs/Makefile.objs @@ -11,6 +11,7 @@ stub-obj-y += gdbstub.o stub-obj-y += get-vm-name.o stub-obj-y += iothread.o stub-obj-y += iothread-lock.o +stub-obj-y += iothread-lock-block.o stub-obj-y += is-daemonized.o stub-obj-$(CONFIG_LINUX_AIO) += linux-aio.o stub-obj-y += machine-init-done.o diff --git a/stubs/iothread-lock-block.c b/stubs/iothread-lock-block.c new file mode 100644 index 0000000000..c88ed70462 --- /dev/null +++ b/stubs/iothread-lock-block.c @@ -0,0 +1,8 @@ +#include "qemu/osdep.h" +#include "qemu/main-loop.h" + +bool qemu_in_main_thread(void) +{ + return qemu_get_current_aio_context() == qemu_get_aio_context(); +} + -- 2.45.1.windows.1