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| author | Florian Weimer <fweimer@redhat.com> | 2019-02-08 12:46:19 +0100 |
|---|---|---|
| committer | Florian Weimer <fweimer@redhat.com> | 2019-02-08 12:46:19 +0100 |
| commit | 669ff911e2571f74a2668493e326ac9a505776bd (patch) | |
| tree | 7cfe768081bfec3d9f9a10cbdd50364ed9ddb1fb /sysdeps/nptl | |
| parent | d0bd87d4c0c11b93f79d1c3531ffb13b4b538190 (diff) | |
| download | glibc-669ff911e2571f74a2668493e326ac9a505776bd.tar.gz | |
nptl: Avoid fork handler lock for async-signal-safe fork [BZ #24161]
Commit 27761a1042daf01987e7d79636d0c41511c6df3c ("Refactor atfork
handlers") introduced a lock, atfork_lock, around fork handler list
accesses. It turns out that this lock occasionally results in
self-deadlocks in malloc/tst-mallocfork2:
(gdb) bt
#0 __lll_lock_wait_private ()
at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:63
#1 0x00007f160c6f927a in __run_fork_handlers (who=(unknown: 209394016),
who@entry=atfork_run_prepare) at register-atfork.c:116
#2 0x00007f160c6b7897 in __libc_fork () at ../sysdeps/nptl/fork.c:58
#3 0x00000000004027d6 in sigusr1_handler (signo=<optimized out>)
at tst-mallocfork2.c:80
#4 sigusr1_handler (signo=<optimized out>) at tst-mallocfork2.c:64
#5 <signal handler called>
#6 0x00007f160c6f92e4 in __run_fork_handlers (who=who@entry=atfork_run_parent)
at register-atfork.c:136
#7 0x00007f160c6b79a2 in __libc_fork () at ../sysdeps/nptl/fork.c:152
#8 0x0000000000402567 in do_test () at tst-mallocfork2.c:156
#9 0x0000000000402dd2 in support_test_main (argc=1, argv=0x7ffc81ef1ab0,
config=config@entry=0x7ffc81ef1970) at support_test_main.c:350
#10 0x0000000000402362 in main (argc=<optimized out>, argv=<optimized out>)
at ../support/test-driver.c:168
If no locking happens in the single-threaded case (where fork is
expected to be async-signal-safe), this deadlock is avoided.
(pthread_atfork is not required to be async-signal-safe, so a fork
call from a signal handler interrupting pthread_atfork is not
a problem.)
Diffstat (limited to 'sysdeps/nptl')
| -rw-r--r-- | sysdeps/nptl/fork.c | 6 | ||||
| -rw-r--r-- | sysdeps/nptl/fork.h | 8 |
2 files changed, 8 insertions, 6 deletions
diff --git a/sysdeps/nptl/fork.c b/sysdeps/nptl/fork.c index bd68f18b45..14b69a6f89 100644 --- a/sysdeps/nptl/fork.c +++ b/sysdeps/nptl/fork.c @@ -55,7 +55,7 @@ __libc_fork (void) but our current fork implementation is not. */ bool multiple_threads = THREAD_GETMEM (THREAD_SELF, header.multiple_threads); - __run_fork_handlers (atfork_run_prepare); + __run_fork_handlers (atfork_run_prepare, multiple_threads); /* If we are not running multiple threads, we do not have to preserve lock state. If fork runs from a signal handler, only @@ -134,7 +134,7 @@ __libc_fork (void) __rtld_lock_initialize (GL(dl_load_lock)); /* Run the handlers registered for the child. */ - __run_fork_handlers (atfork_run_child); + __run_fork_handlers (atfork_run_child, multiple_threads); } else { @@ -149,7 +149,7 @@ __libc_fork (void) } /* Run the handlers registered for the parent. */ - __run_fork_handlers (atfork_run_parent); + __run_fork_handlers (atfork_run_parent, multiple_threads); } return pid; diff --git a/sysdeps/nptl/fork.h b/sysdeps/nptl/fork.h index a1c3b26b68..99ed76034b 100644 --- a/sysdeps/nptl/fork.h +++ b/sysdeps/nptl/fork.h @@ -52,9 +52,11 @@ enum __run_fork_handler_type - atfork_run_child: run all the CHILD_HANDLER and unlocks the internal lock. - atfork_run_parent: run all the PARENT_HANDLER and unlocks the internal - lock. */ -extern void __run_fork_handlers (enum __run_fork_handler_type who) - attribute_hidden; + lock. + + Perform locking only if DO_LOCKING. */ +extern void __run_fork_handlers (enum __run_fork_handler_type who, + _Bool do_locking) attribute_hidden; /* C library side function to register new fork handlers. */ extern int __register_atfork (void (*__prepare) (void), |