Messages in this thread | | | Date | Thu, 11 May 2017 10:11:08 -0700 | From | Guenter Roeck <> | Subject | Threads stuck in zap_pid_ns_processes() |
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Hi all,
the test program attached below almost always results in one of the child processes being stuck in zap_pid_ns_processes(). When this happens, I can see from test logs that nr_hashed == 2 and init_pids==1, but there is only a single thread left in the pid namespace (the one that is stuck). Traceback from /proc/<pid>/stack is
[<ffffffff811c385e>] zap_pid_ns_processes+0x1ee/0x2a0 [<ffffffff810c1ba4>] do_exit+0x10d4/0x1330 [<ffffffff810c1ee6>] do_group_exit+0x86/0x130 [<ffffffff810d4347>] get_signal+0x367/0x8a0 [<ffffffff81046e73>] do_signal+0x83/0xb90 [<ffffffff81004475>] exit_to_usermode_loop+0x75/0xc0 [<ffffffff810055b6>] syscall_return_slowpath+0xc6/0xd0 [<ffffffff81ced488>] entry_SYSCALL_64_fastpath+0xab/0xad [<ffffffffffffffff>] 0xffffffffffffffff
After 120 seconds, I get the "hung task" message.
Example from v4.11:
... [ 3263.379545] INFO: task clone:27910 blocked for more than 120 seconds. [ 3263.379561] Not tainted 4.11.0+ #1 [ 3263.379569] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 3263.379577] clone D 0 27910 27909 0x00000000 [ 3263.379587] Call Trace: [ 3263.379608] __schedule+0x677/0xda0 [ 3263.379621] ? pci_mmcfg_check_reserved+0xc0/0xc0 [ 3263.379634] ? task_stopped_code+0x70/0x70 [ 3263.379643] schedule+0x4d/0xd0 [ 3263.379653] zap_pid_ns_processes+0x1ee/0x2a0 [ 3263.379659] ? copy_pid_ns+0x4d0/0x4d0 [ 3263.379670] do_exit+0x10d4/0x1330 ...
The problem is seen in all kernels up to v4.11.
Any idea what might be going on and how to fix the problem ?
Thanks, Guenter
--- This test program was kindly provided by Vovo Yang <vovoy@google.com>.
Note that the ptrace() call in child1() is not necessary for the problem to be seen, though it seems to make it a bit more likely. ---
#define _GNU_SOURCE #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/ptrace.h> #include <errno.h> #include <string.h> #include <sched.h>
#define STACK_SIZE 65536
int child1(void* arg); int child2(void* arg);
int main(int argc, char **argv) { int child_pid; char* child_stack = malloc(STACK_SIZE); char* stack_top = child_stack + STACK_SIZE; char command[256];
child_pid = clone(&child1, stack_top, CLONE_NEWPID, NULL); if (child_pid == -1) { printf("parent: clone failed: %s\n", strerror(errno)); return EXIT_FAILURE; } printf("parent: child1_pid: %d\n", child_pid);
sleep(2); printf("child state, if it's D (disk sleep), the child process is hung\n"); sprintf(command, "cat /proc/%d/status | grep State:", child_pid); system(command); sleep(3600); return EXIT_SUCCESS; }
int child1(void* arg) { int flags = CLONE_FILES | CLONE_FS | CLONE_VM | CLONE_SIGHAND | CLONE_THREAD; char* child_stack = malloc(STACK_SIZE); char* stack_top = child_stack + STACK_SIZE; long ret;
ret = ptrace(PTRACE_TRACEME, 0, NULL, NULL); if (ret == -1) { printf("child1: ptrace failed: %s\n", strerror(errno)); return EXIT_FAILURE; }
ret = clone(&child2, stack_top, flags, NULL); if (ret == -1) { printf("child1: clone failed: %s\n", strerror(errno)); return EXIT_FAILURE; } printf("child1: child2 pid: %ld\n", ret);
sleep(1); printf("child1: end\n"); return EXIT_SUCCESS; }
int child2(void* arg) { long ret = ptrace(PTRACE_TRACEME, 0, NULL, NULL); if (ret == -1) { printf("child2: ptrace failed: %s\n", strerror(errno)); return EXIT_FAILURE; }
printf("child2: end\n"); return EXIT_SUCCESS; }
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