diff options
Diffstat (limited to 'results/classifier/108/other/1887306')
| -rw-r--r-- | results/classifier/108/other/1887306 | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/results/classifier/108/other/1887306 b/results/classifier/108/other/1887306 new file mode 100644 index 000000000..49d6432be --- /dev/null +++ b/results/classifier/108/other/1887306 @@ -0,0 +1,112 @@ +other: 0.926 +graphic: 0.923 +semantic: 0.901 +performance: 0.900 +debug: 0.895 +permissions: 0.879 +socket: 0.828 +PID: 0.827 +device: 0.810 +boot: 0.799 +files: 0.798 +network: 0.791 +vnc: 0.746 +KVM: 0.742 + +qemu-user deadlocks when forked in a multithreaded process + +The following program (also attached) deadlocks when run under QEMU user on Linux. + +#include <pthread.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/types.h> +#include <sys/wait.h> +#include <unistd.h> + +#define NUM_THREADS 100 +#define NUM_FORKS 10 + +pthread_barrier_t barrier; + +void *t(void *arg) { + for (int i = 0; i < NUM_FORKS; i++) { + pid_t pid = fork(); + if (pid < 0) + abort(); + if (!pid) + _exit(0); + if (waitpid(pid, NULL, 0) < 0) + abort(); + } + //pthread_barrier_wait(&barrier); + return NULL; +} + +int main(void) { + pthread_barrier_init(&barrier, NULL, NUM_THREADS); + pthread_t ts[NUM_THREADS]; + for (size_t i = 0; i < NUM_THREADS; i++) { + if (pthread_create(&ts[i], NULL, t, NULL)) + abort(); + } + for (size_t i = 0; i < NUM_THREADS; i++) { + pthread_join(ts[i], NULL); + } + printf("Done: %d\n", getpid()); + return 0; +} + +To reproduce: +$ gcc test.c -pthread +$ while qemu-x86_64 ./a.out; do :; done + +(Be careful, Ctrl-C/SIGINT doesn't kill the deadlocked child). + +Larger values of NUM_THREADS/NUM_FORKS lead to more often deadlocks. With the values above it often deadlocks on the first try on my machine. When it deadlocks, there is a child qemu process with two threads which is waited upon by one of the worker threads of the parent. + +I tried to avoid the deadlock by serializing fork() with a mutex, but it didn't help. However, ensuring that no thread exits until all forks are done (by adding a barrier to t()) does seem to help, at least, the program above could run for a half an hour until I terminated it. + +Tested on QEMU 5.0.0, 4.2.0 and 2.11.1, with x86_64 and AArch64 linux-user targets. + + + +The QEMU project is currently moving its bug tracking to another system. +For this we need to know which bugs are still valid and which could be +closed already. Thus we are setting the bug state to "Incomplete" now. + +If the bug has already been fixed in the latest upstream version of QEMU, +then please close this ticket as "Fix released". + +If it is not fixed yet and you think that this bug report here is still +valid, then you have two options: + +1) If you already have an account on gitlab.com, please open a new ticket +for this problem in our new tracker here: + + https://gitlab.com/qemu-project/qemu/-/issues + +and then close this ticket here on Launchpad (or let it expire auto- +matically after 60 days). Please mention the URL of this bug ticket on +Launchpad in the new ticket on GitLab. + +2) If you don't have an account on gitlab.com and don't intend to get +one, but still would like to keep this ticket opened, then please switch +the state back to "New" within the next 60 days (otherwise it will get +closed as "Expired"). We will then eventually migrate the ticket auto- +matically to the new system (but you won't be the reporter of the bug +in the new system and thus won't get notified on changes anymore). + +Thank you and sorry for the inconvenience. + + +Still reproduces with QEMU 6.0.0. + + +This is an automated cleanup. This bug report has been moved to QEMU's +new bug tracker on gitlab.com and thus gets marked as 'expired' now. +Please continue with the discussion here: + + https://gitlab.com/qemu-project/qemu/-/issues/358 + + |