Messages in this thread | | | Subject | Strange EFAULT on mips64el returned by syscall when another thread is forking | From | Xi Ruoyao <> | Date | Wed, 24 Jan 2024 18:42:30 +0800 |
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Hi,
When I'm testing Glibc master branch for upcoming 2.39 release, I noticed an alarming test failure on mips64el:
FAIL: stdlib/tst-arc4random-thread
I've gathered some info about it and pasted my findings into https://sourceware.org/glibc/wiki/Testing/Tests/stdlib/tst-arc4random-thread.
Finally I was able to reduce the test case into:
#include <stdlib.h> #include <errno.h> #include <pthread.h> #include <unistd.h> #include <fcntl.h>
void * test_thread (void *) { char buf[16] = {}; int fd = open("/dev/zero", O_RDONLY); while (1) { ssize_t ret = read (fd, buf, 7); if (ret == -1 && errno == EFAULT) abort (); } }
void * fork_thread (void *) { while (1) { if (!fork ()) _exit (0); } }
int main (void) { pthread_t test_th; pthread_t fork_th;
pthread_create (&test_th, NULL, test_thread, NULL); pthread_create (&fork_th, NULL, fork_thread, NULL); pthread_join (test_th, NULL); pthread_join (fork_th, NULL); }
When running this on the mainline kernel (revision 6.8.0-rc1+- g7ed2632ec7d72e926b9e8bcc9ad1bb0cd37274bf) it fails in milliseconds. Some "interesting" aspects:
1. This is related to the size parameter passed to read (). When it's less than 8 it fails, but when it's 8 or greater there is no failure. 2. This is not related to if "buf" is initialized or not.
Now I'm suspecting this might be a kernel bug. Any pointer to further triage?
-- Xi Ruoyao <xry111@xry111.site> School of Aerospace Science and Technology, Xidian University
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