From 7e1711164683b1036f7da5f87c5f66c17a043ab1 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Thu, 27 Jun 2024 20:12:45 +0200 Subject: [PATCH] block/graph-lock: Make WITH_GRAPH_RDLOCK_GUARD() fully checked Upstream clang 18 (and backports to clang 17 in Fedora and RHEL) implemented support for __attribute__((cleanup())) in its Thread Safety Analysis, so we can now actually have a proper implementation of WITH_GRAPH_RDLOCK_GUARD() that understands when we acquire and when we release the lock. -Wthread-safety is now only enabled if the compiler is new enough to understand this pattern. In theory, we could have used some #ifdefs to keep the existing basic checks on old compilers, but as long as someone runs a newer compiler (and our CI does), we will catch locking problems, so it's probably not worth keeping multiple implementations for this. The implementation can't use g_autoptr any more because the glib macros define wrapper functions that don't have the right TSA attributes, so the compiler would complain about them. Just use the cleanup attribute directly instead. Signed-off-by: Kevin Wolf Message-ID: <20240627181245.281403-3-kwolf@redhat.com> Reviewed-by: Stefan Hajnoczi Reviewed-by: Manos Pitsidianakis Signed-off-by: Kevin Wolf --- include/block/graph-lock.h | 21 ++++++++++++++------- meson.build | 14 +++++++++++++- 2 files changed, 27 insertions(+), 8 deletions(-) diff --git a/include/block/graph-lock.h b/include/block/graph-lock.h index d7545e82d0..dc8d949184 100644 --- a/include/block/graph-lock.h +++ b/include/block/graph-lock.h @@ -209,31 +209,38 @@ typedef struct GraphLockable { } GraphLockable; * unlocked. TSA_ASSERT_SHARED() makes sure that the following calls know that * we hold the lock while unlocking is left unchecked. */ -static inline GraphLockable * TSA_ASSERT_SHARED(graph_lock) TSA_NO_TSA coroutine_fn +static inline GraphLockable * TSA_ACQUIRE_SHARED(graph_lock) coroutine_fn graph_lockable_auto_lock(GraphLockable *x) { bdrv_graph_co_rdlock(); return x; } -static inline void TSA_NO_TSA coroutine_fn -graph_lockable_auto_unlock(GraphLockable *x) +static inline void TSA_RELEASE_SHARED(graph_lock) coroutine_fn +graph_lockable_auto_unlock(GraphLockable **x) { bdrv_graph_co_rdunlock(); } -G_DEFINE_AUTOPTR_CLEANUP_FUNC(GraphLockable, graph_lockable_auto_unlock) +#define GRAPH_AUTO_UNLOCK __attribute__((cleanup(graph_lockable_auto_unlock))) +/* + * @var is only used to break the loop after the first iteration. + * @unlock_var can't be unlocked and then set to NULL because TSA wants the lock + * to be held at the start of every iteration of the loop. + */ #define WITH_GRAPH_RDLOCK_GUARD_(var) \ - for (g_autoptr(GraphLockable) var = graph_lockable_auto_lock(GML_OBJ_()); \ + for (GraphLockable *unlock_var GRAPH_AUTO_UNLOCK = \ + graph_lockable_auto_lock(GML_OBJ_()), \ + *var = unlock_var; \ var; \ - graph_lockable_auto_unlock(var), var = NULL) + var = NULL) #define WITH_GRAPH_RDLOCK_GUARD() \ WITH_GRAPH_RDLOCK_GUARD_(glue(graph_lockable_auto, __COUNTER__)) #define GRAPH_RDLOCK_GUARD(x) \ - g_autoptr(GraphLockable) \ + GraphLockable * GRAPH_AUTO_UNLOCK \ glue(graph_lockable_auto, __COUNTER__) G_GNUC_UNUSED = \ graph_lockable_auto_lock(GML_OBJ_()) diff --git a/meson.build b/meson.build index 97f63aa86c..c2a050b844 100644 --- a/meson.build +++ b/meson.build @@ -649,7 +649,19 @@ warn_flags = [ ] if host_os != 'darwin' - warn_flags += ['-Wthread-safety'] + tsa_has_cleanup = cc.compiles(''' + struct __attribute__((capability("mutex"))) mutex {}; + void lock(struct mutex *m) __attribute__((acquire_capability(m))); + void unlock(struct mutex *m) __attribute__((release_capability(m))); + + void test(void) { + struct mutex __attribute__((cleanup(unlock))) m; + lock(&m); + } + ''', args: ['-Wthread-safety', '-Werror']) + if tsa_has_cleanup + warn_flags += ['-Wthread-safety'] + endif endif # Set up C++ compiler flags