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Date: Sat, 08 Oct 2022 20:03:24 +0300
From: Alexey Izbyshev <izbyshev@...ras.ru>
To: musl@...ts.openwall.com
Subject: Re: MT fork and key_lock in pthread_key_create.c
On 2022-10-08 04:36, Rich Felker wrote:
> On Thu, Oct 06, 2022 at 02:21:51PM -0400, Rich Felker wrote:
>> On Thu, Oct 06, 2022 at 09:37:50AM +0300, Alexey Izbyshev wrote:
>> > Hi,
>> >
>> > I noticed that fork() doesn't take key_lock that is used to protect
>> > the global table of thread-specific keys. I couldn't find mentions
>> > of this lock in the MT fork discussion in the mailing list archive.
>> > Was this lock overlooked?
>>
>> I think what happened was that we made the main list of locks to
>> review and take care of via grep for LOCK, and then manually added
>> known instances of locks using other locking primitives. This one must
>> have been missed.
>>
>> Having special-case lock types like this is kinda a pain, but as long
>> as there aren't too many I guess it's not a big deal.
>
> Proposed patch attached.
diff --git a/src/internal/fork_impl.h b/src/internal/fork_impl.h
index ae3a79e5..354e733b 100644
--- a/src/internal/fork_impl.h
+++ b/src/internal/fork_impl.h
@@ -16,3 +16,4 @@ extern hidden volatile int *const __vmlock_lockptr;
hidden void __malloc_atfork(int);
hidden void __ldso_atfork(int);
+hidden void __pthread_key_atfork(int);
diff --git a/src/process/fork.c b/src/process/fork.c
index 80e804b1..56f19313 100644
--- a/src/process/fork.c
+++ b/src/process/fork.c
@@ -37,6 +37,7 @@ static void dummy(int x) { }
weak_alias(dummy, __fork_handler);
weak_alias(dummy, __malloc_atfork);
weak_alias(dummy, __aio_atfork);
+weak_alias(dummy, __pthread_key_atfork);
weak_alias(dummy, __ldso_atfork);
static void dummy_0(void) { }
@@ -51,6 +52,7 @@ pid_t fork(void)
int need_locks = libc.need_locks > 0;
if (need_locks) {
__ldso_atfork(-1);
+ __pthread_key_atfork(-1);
__aio_atfork(-1);
__inhibit_ptc();
for (int i=0; i<sizeof atfork_locks/sizeof *atfork_locks; i++)
@@ -78,6 +80,7 @@ pid_t fork(void)
else **atfork_locks[i] = 0;
__release_ptc();
if (ret) __aio_atfork(0);
+ __pthread_key_atfork(!ret);
__ldso_atfork(!ret);
}
__restore_sigs(&set);
diff --git a/src/thread/pthread_key_create.c
b/src/thread/pthread_key_create.c
index d1120941..39770c7a 100644
--- a/src/thread/pthread_key_create.c
+++ b/src/thread/pthread_key_create.c
@@ -1,4 +1,5 @@
#include "pthread_impl.h"
+#include "fork_impl.h"
volatile size_t __pthread_tsd_size = sizeof(void *) * PTHREAD_KEYS_MAX;
void *__pthread_tsd_main[PTHREAD_KEYS_MAX] = { 0 };
@@ -20,6 +21,13 @@ static void dummy_0(void)
weak_alias(dummy_0, __tl_lock);
weak_alias(dummy_0, __tl_unlock);
+void __pthread_key_atfork(int who)
+{
+ if (who<0) __pthread_rwlock_rdlock(&key_lock);
+ else if (!who) __pthread_rwlock_unlock(&key_lock);
+ else key_lock = (pthread_rwlock_t)PTHREAD_RWLOCK_INITIALIZER;
Are you using PTHREAD_RWLOCK_INITIALIZER to avoid dependency on
pthread_rwlock_init (which is used in the aio_atfork patch[1])?
[1] https://www.openwall.com/lists/musl/2022/10/06/5
+}
+
int __pthread_key_create(pthread_key_t *k, void (*dtor)(void *))
{
pthread_t self = __pthread_self();
Looks good to me otherwise.
Thanks,
Alexey
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