This is a note to let you know that I've just added the patch titled
pidfd: fix test failure due to stack overflow on some arches
to the 5.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
pidfd-fix-test-failure-due-to-stack-overflow-on-some.patch
and it can be found in the queue-5.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ed7009f08f9612ed8a2522ac9c7f8e1080cd5644
Author: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Date: Thu Jan 27 13:29:51 2022 -0800
pidfd: fix test failure due to stack overflow on some arches
[ Upstream commit 4cbd93c3c110447adc66cb67c08af21f939ae2d7 ]
When running the pidfd_fdinfo_test on arm64, it fails for me. After some
digging, the reason is that the child exits due to SIGBUS, because it
overflows the 1024 byte stack we've reserved for it.
To fix the issue, increase the stack size to 8192 bytes (this number is
somewhat arbitrary, and was arrived at through experimentation -- I kept
doubling until the failure no longer occurred).
Also, let's make the issue easier to debug. wait_for_pid() returns an
ambiguous value: it may return -1 in all of these cases:
1. waitpid() itself returned -1
2. waitpid() returned success, but we found !WIFEXITED(status).
3. The child process exited, but it did so with a -1 exit code.
There's no way for the caller to tell the difference. So, at least log
which occurred, so the test runner can debug things.
While debugging this, I found that we had !WIFEXITED(), because the
child exited due to a signal. This seems like a reasonably common case,
so also print out whether or not we have WIFSIGNALED(), and the
associated WTERMSIG() (if any). This lets us see the SIGBUS I'm fixing
clearly when it occurs.
Finally, I'm suspicious of allocating the child's stack on our stack.
man clone(2) suggests that the correct way to do this is with mmap(),
and in particular by setting MAP_STACK. So, switch to doing it that way
instead.
Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Acked-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 01f8d3c0cf2cb..6922d6417e1cf 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -68,7 +68,7 @@
#define PIDFD_SKIP 3
#define PIDFD_XFAIL 4
-int wait_for_pid(pid_t pid)
+static inline int wait_for_pid(pid_t pid)
{
int status, ret;
@@ -78,13 +78,20 @@ int wait_for_pid(pid_t pid)
if (errno == EINTR)
goto again;
+ ksft_print_msg("waitpid returned -1, errno=%d\n", errno);
return -1;
}
- if (!WIFEXITED(status))
+ if (!WIFEXITED(status)) {
+ ksft_print_msg(
+ "waitpid !WIFEXITED, WIFSIGNALED=%d, WTERMSIG=%d\n",
+ WIFSIGNALED(status), WTERMSIG(status));
return -1;
+ }
- return WEXITSTATUS(status);
+ ret = WEXITSTATUS(status);
+ ksft_print_msg("waitpid WEXITSTATUS=%d\n", ret);
+ return ret;
}
static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
diff --git a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
index 22558524f71c3..3fd8e903118f5 100644
--- a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
@@ -12,6 +12,7 @@
#include <string.h>
#include <syscall.h>
#include <sys/wait.h>
+#include <sys/mman.h>
#include "pidfd.h"
#include "../kselftest.h"
@@ -80,7 +81,10 @@ static inline int error_check(struct error *err, const char *test_name)
return err->code;
}
+#define CHILD_STACK_SIZE 8192
+
struct child {
+ char *stack;
pid_t pid;
int fd;
};
@@ -89,17 +93,22 @@ static struct child clone_newns(int (*fn)(void *), void *args,
struct error *err)
{
static int flags = CLONE_PIDFD | CLONE_NEWPID | CLONE_NEWNS | SIGCHLD;
- size_t stack_size = 1024;
- char *stack[1024] = { 0 };
struct child ret;
if (!(flags & CLONE_NEWUSER) && geteuid() != 0)
flags |= CLONE_NEWUSER;
+ ret.stack = mmap(NULL, CHILD_STACK_SIZE, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+ if (ret.stack == MAP_FAILED) {
+ error_set(err, -1, "mmap of stack failed (errno %d)", errno);
+ return ret;
+ }
+
#ifdef __ia64__
- ret.pid = __clone2(fn, stack, stack_size, flags, args, &ret.fd);
+ ret.pid = __clone2(fn, ret.stack, CHILD_STACK_SIZE, flags, args, &ret.fd);
#else
- ret.pid = clone(fn, stack + stack_size, flags, args, &ret.fd);
+ ret.pid = clone(fn, ret.stack + CHILD_STACK_SIZE, flags, args, &ret.fd);
#endif
if (ret.pid < 0) {
@@ -129,6 +138,11 @@ static inline int child_join(struct child *child, struct error *err)
else if (r > 0)
error_set(err, r, "child %d reported: %d", child->pid, r);
+ if (munmap(child->stack, CHILD_STACK_SIZE)) {
+ error_set(err, -1, "munmap of child stack failed (errno %d)", errno);
+ r = -1;
+ }
+
return r;
}
