musl - musl - an implementation of the standard library for Linux-based systems

musl - an implementation of the standard library for Linux-based systems

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author	Rich Felker <dalias@aerifal.cx>	2024年07月24日 12:33:46 -0400
committer	Rich Felker <dalias@aerifal.cx>	2024年07月24日 12:33:46 -0400
commit	9ee6f104075fa6c37bb57a4ef406f3ff290b586c (patch)
tree	787fc5423a68c66a6f31c3e9adca570688400b6f /src
parent	8cca79a72cccbdb54726125d690d7d0095fc2409 (diff)
download	musl-9ee6f104075fa6c37bb57a4ef406f3ff290b586c.tar.gz

atexit: fail rather than deadlocking after last handler is called

previously, global dtors, which are executed after all atexit handlers have been called rather than being implemented as an atexit handler themselves, would deadlock if they called atexit. it was intentional to disallow adding more atexit handlers past the last point where they would be executed, since a successful return from atexit imposes a contract that the handler will be executed, but this was only considered in the context of calls to atexit from other threads, not calls from the dtors. to fix this, release the lock after the exit handlers loop completes, but but set a flag first so that we can make all future calls to atexit return a failure code.

Diffstat (limited to 'src')

-rw-r--r--

src/exit/atexit.c

1 files changed, 12 insertions, 0 deletions

diff --git a/src/exit/atexit.c b/src/exit/atexit.c
index 854e9fdd..92c91c9d 100644
--- a/src/exit/atexit.c
+++ b/src/exit/atexit.c

@@ -19,6 +19,7 @@ static struct fl

void *a[COUNT];

} builtin, *head;

+static int finished_atexit;

static int slot;

static volatile int lock[1];

volatile int *const __atexit_lockptr = lock;

@@ -34,6 +35,10 @@ void __funcs_on_exit()

func(arg);

LOCK(lock);

}

+ /* Unlock to prevent deadlock if a global dtor

+ * attempts to call atexit. */

+ finished_atexit = 1;

+ UNLOCK(lock);

}

void __cxa_finalize(void *dso)

@@ -44,6 +49,13 @@ int __cxa_atexit(void (*func)(void *), void *arg, void *dso)

{

LOCK(lock);

+ /* Prevent dtors from registering further atexit

+ * handlers that would never be run. */

+ if (finished_atexit) {

+ UNLOCK(lock);

+ return -1;

+ }

/* Defer initialization of head so it can be in BSS */

if (!head) head = &builtin;

generated by cgit v1.2.1 (git 2.18.0) at 2025年09月21日 23:04:17 +0000