[RFC PATCH for 4.21 01/16] rseq/selftests: Expose reference counter to coexist with glibc (v2)
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2018-11-01 09:59:08
Also in:
lkml
Subsystem:
kernel selftest framework, restartable sequences support, the rest · Maintainers:
Shuah Khan, Shuah Khan, Mathieu Desnoyers, Peter Zijlstra, "Paul E. McKenney", Boqun Feng, Linus Torvalds
In order to integrate rseq into user-space applications, expose a reference counter TLS as a __rseq_refcount weak symbol so many rseq users can be linked into the same application (e.g. librseq and glibc). The reference count ensures that rseq syscall registration/unregistration happens only for the most early/late user for each thread, thus ensuring that rseq is registered across the lifetime of all rseq users for a given thread. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: Shuah Khan <shuah@kernel.org> CC: Carlos O'Donell <redacted> CC: Florian Weimer <redacted> CC: Joseph Myers <redacted> CC: Szabolcs Nagy <redacted> CC: Thomas Gleixner <redacted> CC: Ben Maurer <redacted> CC: Peter Zijlstra <peterz@infradead.org> CC: "Paul E. McKenney" <redacted> CC: Boqun Feng <redacted> CC: Will Deacon <redacted> CC: Dave Watson <redacted> CC: Paul Turner <redacted> CC: linux-api@vger.kernel.org --- Changes since v1: - Error out on refcount overflow/underflow. - Expose __rseq_refcount weak symbol. --- tools/testing/selftests/rseq/rseq.c | 23 ++++++++++++++++------- tools/testing/selftests/rseq/rseq.h | 1 + 2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..835e3917d220 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c@@ -25,18 +25,19 @@ #include <syscall.h> #include <assert.h> #include <signal.h> +#include <limits.h> #include "rseq.h" #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0])) -__attribute__((tls_model("initial-exec"))) __thread +__attribute__((weak)) __thread volatile struct rseq __rseq_abi = { .cpu_id = RSEQ_CPU_ID_UNINITIALIZED, }; -static __attribute__((tls_model("initial-exec"))) __thread -volatile int refcount; +__attribute__((weak)) __thread +volatile uint32_t __rseq_refcount; static void signal_off_save(sigset_t *oldset) {
@@ -70,7 +71,11 @@ int rseq_register_current_thread(void) sigset_t oldset; signal_off_save(&oldset); - if (refcount++) + if (__rseq_refcount == UINT_MAX) { + ret = -1; + goto end; + } + if (__rseq_refcount++) goto end; rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG); if (!rc) {
@@ -78,9 +83,9 @@ int rseq_register_current_thread(void) goto end; } if (errno != EBUSY) - __rseq_abi.cpu_id = -2; + __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED; ret = -1; - refcount--; + __rseq_refcount--; end: signal_restore(oldset); return ret;
@@ -92,7 +97,11 @@ int rseq_unregister_current_thread(void) sigset_t oldset; signal_off_save(&oldset); - if (--refcount) + if (!__rseq_refcount) { + ret = -1; + goto end; + } + if (--__rseq_refcount) goto end; rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index c72eb70f9b52..47f815c19cef 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h@@ -45,6 +45,7 @@ #endif extern __thread volatile struct rseq __rseq_abi; +extern __thread volatile uint32_t __rseq_refcount; #define rseq_likely(x) __builtin_expect(!!(x), 1) #define rseq_unlikely(x) __builtin_expect(!!(x), 0)
--
2.11.0