[RFC PATCH for 5.2 03/10] rseq/selftests: Use __rseq_handled symbol to coexist with glibc
STALE2715d
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2019-04-24 15:26:03
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
Revision rfc of 2 in this series.
Revisions (2)
- rfc current
- v1 [diff vs current]
In order to integrate rseq into user-space applications, expose a
__rseq_handled symbol so many rseq users can be linked into the same
application (e.g. librseq and glibc).
The __rseq_refcount TLS variable is static to the librseq library. It
ensures that rseq syscall registration/unregistration happens only for
the most early/late caller to rseq_{,un}register_current_thread 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
---
tools/testing/selftests/rseq/rseq.c | 55 +++++++++++++++++++++++++++++++------
tools/testing/selftests/rseq/rseq.h | 1 +
2 files changed, 48 insertions(+), 8 deletions(-)
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..d44cc17ad929 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c@@ -25,18 +25,27 @@ #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 -volatile struct rseq __rseq_abi = { +__thread volatile struct rseq __rseq_abi = { .cpu_id = RSEQ_CPU_ID_UNINITIALIZED, }; -static __attribute__((tls_model("initial-exec"))) __thread -volatile int refcount; +/* + * Shared with other libraries. This library may take rseq ownership if it is + * still 0 when executing the library constructor. Set to 1 by library + * constructor when handling rseq. Set to 0 in destructor if handling rseq. + */ +int __rseq_handled; + +/* Whether this library have ownership of rseq registration. */ +static int rseq_ownership; + +static __thread volatile uint32_t __rseq_refcount; static void signal_off_save(sigset_t *oldset) {
@@ -69,8 +78,14 @@ int rseq_register_current_thread(void) int rc, ret = 0; sigset_t oldset; + if (!rseq_ownership) + return 0; 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 +93,9 @@ 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_lib_abi.refcount--; end: signal_restore(oldset); return ret;
@@ -91,13 +106,20 @@ int rseq_unregister_current_thread(void) int rc, ret = 0; sigset_t oldset; + if (!rseq_ownership) + return 0; 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); if (!rc) goto end; + __rseq_refcount = 1; ret = -1; end: signal_restore(oldset);
@@ -115,3 +137,20 @@ int32_t rseq_fallback_current_cpu(void) } return cpu; } + +void __attribute__((constructor)) rseq_init(void) +{ + /* Check whether rseq is handled by another library. */ + if (__rseq_handled) + return; + __rseq_handled = 1; + rseq_ownership = 1; +} + +void __attribute__((destructor)) rseq_fini(void) +{ + if (!rseq_ownership) + return; + __rseq_handled = 0; + rseq_ownership = 0; +}
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index c72eb70f9b52..26348e2c44f3 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 int __rseq_handled; #define rseq_likely(x) __builtin_expect(!!(x), 1) #define rseq_unlikely(x) __builtin_expect(!!(x), 0)
--
2.11.0