From patchwork Wed Jun 3 06:44:58 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexandre Oliva X-Patchwork-Id: 7023 Received: (qmail 13516 invoked by alias); 3 Jun 2015 06:45:42 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 13495 invoked by uid 89); 3 Jun 2015 06:45:37 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.0 required=5.0 tests=AWL, BAYES_50, KAM_LAZY_DOMAIN_SECURITY, SPF_HELO_PASS, T_RP_MATCHES_RCVD autolearn=no version=3.3.2 X-HELO: mx1.redhat.com From: Alexandre Oliva To: libc-alpha@sourceware.org Subject: [PR18457] Don't require rtld lock to compute DTV addr for static TLS Date: Wed, 03 Jun 2015 03:44:58 -0300 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 We used to store static TLS addrs in the DTV at module load time, but this required one thread to modify another thread's DTV. Now that we defer the DTV update to the first use in the thread, we should do so without taking the rtld lock if the module is already assigned to static TLS. Taking the lock introduces deadlocks where there weren't any before. This patch fixes the deadlock caused by tls_get_addr's unnecessarily taking the rtld lock to initialize the DTV entry for tls_dtor_list within __call_dtors_list, which deadlocks with a dlclose of a module whose finalizer joins with that thread. The patch does not, however, attempt to fix other potential sources of similar deadlocks, such as the explicit rtld locks taken by call_dtors_list, when the dtor list is not empty; lazy relocation of the reference to tls_dtor_list, when TLS Descriptors are in use; when tls dtors call functions through the PLT and lazy relocation needs to be performed, or any such called functions interact with the dynamic loader in ways that require its lock to be taken. Ok to install? for ChangeLog [PR dynamic-link/18457] * elf/dl-tls.c (tls_get_addr_tail): Don't take the rtld lock if we already have a final static TLS offset. * nptl/tst-join7.c, nptl/tst-join7mod.c: New. --- NEWS | 2 +- elf/dl-tls.c | 38 ++++++++++++++++++++++++++------------ nptl/Makefile | 10 ++++++++-- nptl/tst-join7.c | 12 ++++++++++++ nptl/tst-join7mod.c | 29 +++++++++++++++++++++++++++++ 5 files changed, 76 insertions(+), 15 deletions(-) create mode 100644 nptl/tst-join7.c create mode 100644 nptl/tst-join7mod.c diff --git a/NEWS b/NEWS index ed02de0..eac100c 100644 --- a/NEWS +++ b/NEWS @@ -19,7 +19,7 @@ Version 2.22 18047, 18049, 18068, 18080, 18093, 18100, 18104, 18110, 18111, 18116, 18125, 18128, 18138, 18185, 18196, 18197, 18206, 18210, 18211, 18217, 18220, 18221, 18234, 18244, 18247, 18287, 18319, 18333, 18346, 18397, - 18409, 18410, 18412, 18418, 18422, 18434, 18444, 18469. + 18409, 18410, 18412, 18418, 18422, 18434, 18444, 18457, 18469. * Cache information can be queried via sysconf() function on s390 e.g. with _SC_LEVEL1_ICACHE_SIZE as argument. diff --git a/elf/dl-tls.c b/elf/dl-tls.c index 20c7e33..726f1ea 100644 --- a/elf/dl-tls.c +++ b/elf/dl-tls.c @@ -755,30 +755,44 @@ tls_get_addr_tail (GET_ADDR_ARGS, dtv_t *dtv, struct link_map *the_map) the_map = listp->slotinfo[idx].map; } - /* Make sure that, if a dlopen running in parallel forces the - variable into static storage, we'll wait until the address in the - static TLS block is set up, and use that. If we're undecided - yet, make sure we make the decision holding the lock as well. */ - if (__glibc_unlikely (the_map->l_tls_offset - != FORCED_DYNAMIC_TLS_OFFSET)) + /* If the TLS block for the map is already assigned to dynamic or to + static TLS, avoid the lock. Be careful to use the same value for + both tests; if we reloaded it, the second test might mistake + forced dynamic for an offset. Now, if the decision hasn't been + made, take the rtld lock, so that an ongoing dlopen gets a chance + to complete, and then retest; if the decision is still pending, + force the module to dynamic TLS. */ + ptrdiff_t offset = atomic_load_relaxed (&the_map->l_tls_offset); + if (__glibc_unlikely (offset != FORCED_DYNAMIC_TLS_OFFSET)) { + if (__glibc_unlikely (offset != NO_TLS_OFFSET)) + goto static_tls; __rtld_lock_lock_recursive (GL(dl_load_lock)); - if (__glibc_likely (the_map->l_tls_offset == NO_TLS_OFFSET)) + offset = the_map->l_tls_offset; + if (__glibc_likely (offset == NO_TLS_OFFSET)) { the_map->l_tls_offset = FORCED_DYNAMIC_TLS_OFFSET; __rtld_lock_unlock_recursive (GL(dl_load_lock)); } - else if (__glibc_likely (the_map->l_tls_offset - != FORCED_DYNAMIC_TLS_OFFSET)) + else if (__glibc_likely (offset != FORCED_DYNAMIC_TLS_OFFSET)) { + /* The decision is made, and it is final. We use the value + we've already loaded, but we could even load the offset + after releasing the lock, since it won't change. Should + the module be released while another thread references + one of its TLS variables, that's undefined behavior. */ + __rtld_lock_unlock_recursive (GL(dl_load_lock)); + + static_tls: + ; + #if TLS_TCB_AT_TP - void *p = (char *) THREAD_SELF - the_map->l_tls_offset; + void *p = (char *) THREAD_SELF - offset; #elif TLS_DTV_AT_TP - void *p = (char *) THREAD_SELF + the_map->l_tls_offset + TLS_PRE_TCB_SIZE; + void *p = (char *) THREAD_SELF + offset + TLS_PRE_TCB_SIZE; #else # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined" #endif - __rtld_lock_unlock_recursive (GL(dl_load_lock)); dtv[GET_ADDR_MODULE].pointer.is_static = true; dtv[GET_ADDR_MODULE].pointer.val = p; diff --git a/nptl/Makefile b/nptl/Makefile index 3dd2944..4ffd13c 100644 --- a/nptl/Makefile +++ b/nptl/Makefile @@ -242,7 +242,7 @@ tests = tst-typesizes \ tst-basic7 \ tst-kill1 tst-kill2 tst-kill3 tst-kill4 tst-kill5 tst-kill6 \ tst-raise1 \ - tst-join1 tst-join2 tst-join3 tst-join4 tst-join5 tst-join6 \ + tst-join1 tst-join2 tst-join3 tst-join4 tst-join5 tst-join6 tst-join7 \ tst-detach1 \ tst-eintr1 tst-eintr2 tst-eintr3 tst-eintr4 tst-eintr5 \ tst-tsd1 tst-tsd2 tst-tsd3 tst-tsd4 tst-tsd5 tst-tsd6 \ @@ -320,7 +320,8 @@ endif modules-names = tst-atfork2mod tst-tls3mod tst-tls4moda tst-tls4modb \ tst-tls5mod tst-tls5moda tst-tls5modb tst-tls5modc \ tst-tls5modd tst-tls5mode tst-tls5modf tst-stack4mod \ - tst-_res1mod1 tst-_res1mod2 tst-execstack-mod tst-fini1mod + tst-_res1mod1 tst-_res1mod2 tst-execstack-mod tst-fini1mod \ + tst-join7mod extra-test-objs += $(addsuffix .os,$(strip $(modules-names))) tst-cleanup4aux.o test-extras += $(modules-names) tst-cleanup4aux test-modules = $(addprefix $(objpfx),$(addsuffix .so,$(modules-names))) @@ -525,6 +526,11 @@ $(objpfx)tst-tls6.out: tst-tls6.sh $(objpfx)tst-tls5 \ $(evaluate-test) endif +$(objpfx)tst-join7: $(libdl) $(shared-thread-library) +$(objpfx)tst-join7.out: $(objpfx)tst-join7mod.so +$(objpfx)tst-join7mod.so: $(shared-thread-library) +LDFLAGS-tst-join7mod.so = -Wl,-soname,tst-join7mod.so + $(objpfx)tst-dlsym1: $(libdl) $(shared-thread-library) $(objpfx)tst-fini1: $(shared-thread-library) $(objpfx)tst-fini1mod.so diff --git a/nptl/tst-join7.c b/nptl/tst-join7.c new file mode 100644 index 0000000..bf6fc76 --- /dev/null +++ b/nptl/tst-join7.c @@ -0,0 +1,12 @@ +#include + +int +do_test (void) +{ + void *f = dlopen ("tst-join7mod.so", RTLD_NOW | RTLD_GLOBAL); + if (f) dlclose (f); else return 1; + return 0; +} + +#define TEST_FUNCTION do_test () +#include "../test-skeleton.c" diff --git a/nptl/tst-join7mod.c b/nptl/tst-join7mod.c new file mode 100644 index 0000000..a8c7bc0 --- /dev/null +++ b/nptl/tst-join7mod.c @@ -0,0 +1,29 @@ +#include +#include + +static pthread_t th; +static int running = 1; + +static void * +test_run (void *p) +{ + while (running) + fprintf (stderr, "XXX test_run\n"); + fprintf (stderr, "XXX test_run FINISHED\n"); + return NULL; +} + +static void __attribute__ ((constructor)) +do_init (void) +{ + pthread_create (&th, NULL, test_run, NULL); +} + +static void __attribute__ ((destructor)) +do_end (void) +{ + running = 0; + fprintf (stderr, "thread_join...\n"); + pthread_join (th, NULL); + fprintf (stderr, "thread_join DONE\n"); +}