From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: [RFC PATCH for 4.21 01/16] rseq/selftests: Expose reference counter to coexist with glibc (v2) Date: Thu, 1 Nov 2018 10:58:29 +0100 Message-ID: <20181101095844.24462-2-mathieu.desnoyers@efficios.com> References: <20181101095844.24462-1-mathieu.desnoyers@efficios.com> Return-path: In-Reply-To: <20181101095844.24462-1-mathieu.desnoyers@efficios.com> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra , "Paul E . McKenney" , Boqun Feng Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Thomas Gleixner , Andy Lutomirski , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H . Peter Anvin" , Andi Kleen , Chris Lameter , Ben Maurer , Steven Rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , Mathieu Desnoyers List-Id: linux-api@vger.kernel.org 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 CC: Shuah Khan CC: Carlos O'Donell CC: Florian Weimer CC: Joseph Myers CC: Szabolcs Nagy CC: Thomas Gleixner CC: Ben Maurer CC: Peter Zijlstra CC: "Paul E. McKenney" CC: Boqun Feng CC: Will Deacon CC: Dave Watson CC: Paul Turner 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 #include #include +#include #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