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I think the hang happens here in epoll_wait():
=======
(gdb) up
#1 0x0000003727a0534b in ply_event_loop_process_pending_events (loop=0x608010) at ply-event-loop.c:1276
1276 number_of_received_events = epoll_wait (loop->epoll_fd, events,
(gdb) l
1271 {
1272 timeout = (int) ((loop->wakeup_time - ply_get_timestamp ()) * 1000);
1273 timeout = MAX (timeout, 0);
1274 }
1275
1276 number_of_received_events = epoll_wait (loop->epoll_fd, events,
1277 sizeof (events), timeout);
=======
Here, timeout is 0 and loop->epoll_fd points to:
6.7 S x86_64 # ls -l /proc/20862/fd/7
lrwx------ 1 root root 64 Sep 15 06:08 /proc/20862/fd/7 -> [eventpoll]
Comment 3Ray Strode [halfline]
2015-09-15 13:31:44 UTC
is it looping ? a timeout of 0 to epoll_wait() should return immediately.
plymouth --details is a command that is run when there is a failure. I wonder if this stall is the cause of your problem or just a side effect. Do you see anything strange in dmesg ?
Comment 6Ray Strode [halfline]
2015-09-21 17:29:48 UTC
okay let's close this one out since we don't have a customer complaining and it's not clear we'll be able to debug the problem without a reproduction environment.
On my rhel-6.7 test box I was attempting to do a `service avahi-daemon restart` and noticed it "stalls". Strace shows that the stall is caused by `/bin/plymouth --details`. Versions used: plymouth-0.8.3-27.el6_5.1.x86_64, glibc-2.12-1.166.el6.x86_64. Strace log: ======= strace -f /bin/plymouth --details ... stuff deleted ... open("/lib64/libpthread.so.0", O_RDONLY) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340]\340&7\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=145896, ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f913f9a4000 mmap(0x3726e00000, 2212848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3726e00000 mprotect(0x3726e17000, 2097152, PROT_NONE) = 0 mmap(0x3727017000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x3727017000 mmap(0x3727019000, 13296, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3727019000 close(3) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f913f9a3000 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f913f9a2000 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f913f9a1000 arch_prctl(ARCH_SET_FS, 0x7f913f9a2700) = 0 mprotect(0x3727882000, 4096, PROT_READ) = 0 mprotect(0x3727406000, 4096, PROT_READ) = 0 mprotect(0x3726802000, 4096, PROT_READ) = 0 mprotect(0x3726d8a000, 16384, PROT_READ) = 0 mprotect(0x3727017000, 4096, PROT_READ) = 0 mprotect(0x372641f000, 4096, PROT_READ) = 0 munmap(0x7f913f9a6000, 63724) = 0 set_tid_address(0x7f913f9a29d0) = 14880 set_robust_list(0x7f913f9a29e0, 24) = 0 futex(0x7fffe4fe5c8c, FUTEX_WAKE_PRIVATE, 1) = 0 futex(0x7fffe4fe5c8c, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 1, NULL, 7f913f9a2700) = -1 EAGAIN (Resource temporarily unavailable) rt_sigaction(SIGRTMIN, {0x3726e05c60, [], SA_RESTORER|SA_SIGINFO, 0x3726e0f790}, NULL, 8) = 0 rt_sigaction(SIGRT_1, {0x3726e05cf0, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x3726e0f790}, NULL, 8) = 0 rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0 getrlimit(RLIMIT_STACK, {rlim_cur=10240*1024, rlim_max=RLIM64_INFINITY}) = 0 rt_sigaction(SIGPIPE, {SIG_IGN, [PIPE], SA_RESTORER|SA_RESTART, 0x3726a326a0}, {SIG_DFL, [], 0}, 8) = 0 brk(0) = 0x1192000 brk(0x11b3000) = 0x11b3000 epoll_create(64) = 3 pipe([4, 5]) = 0 fcntl(4, F_SETFD, FD_CLOEXEC|0x800) = 0 fcntl(5, F_SETFD, FD_CLOEXEC|0x800) = 0 epoll_ctl(3, EPOLL_CTL_ADD, 4, {EPOLLERR|EPOLLHUP, {u32=18424048, u64=18424048}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 4, {EPOLLIN|EPOLLERR|EPOLLHUP, {u32=18424048, u64=18424048}}) = 0 open("proc/cmdline", O_RDONLY) = -1 ENOENT (No such file or directory) socket(PF_LOCAL, SOCK_STREAM, 0) = 6 fcntl(6, F_SETFD, FD_CLOEXEC|0x800) = 0 setsockopt(6, SOL_SOCKET, SO_PASSCRED, [1], 4) = 0 connect(6, {sa_family=AF_LOCAL, sun_path=@"/ply-boot-protocol"}, 110) = 0 epoll_ctl(3, EPOLL_CTL_ADD, 6, {EPOLLERR|EPOLLHUP, {u32=18436912, u64=18436912}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLERR|EPOLLHUP, {u32=18436912, u64=18436912}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLOUT|EPOLLERR|EPOLLHUP, {u32=18436912, u64=18436912}}) = 0 epoll_wait(3, {{EPOLLOUT, {u32=18436912, u64=18436912}}}, 8, -1) = 1 write(6, "!\0", 2) = 2 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLIN|EPOLLOUT|EPOLLERR|EPOLLHUP, {u32=18436912, u64=18436912}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLIN|EPOLLERR|EPOLLHUP, {u32=18436912, u64=18436912}}) = 0 epoll_wait(3, ======= Traceback: ======= 6.7 S x86_64 # gdb -q -args /bin/plymouth --details Reading symbols from /bin/plymouth...Reading symbols from /usr/lib/debug/bin/plymouth.debug...done. done. (gdb) r Starting program: /bin/plymouth --details [Thread debugging using libthread_db enabled] ^C Program received signal SIGINT, Interrupt. 0x0000003726ae8f43 in __epoll_wait_nocancel () at ../sysdeps/unix/syscall-template.S:82 82 T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS) (gdb) bt #0 0x0000003726ae8f43 in __epoll_wait_nocancel () at ../sysdeps/unix/syscall-template.S:82 #1 0x0000003727a0534b in ply_event_loop_process_pending_events (loop=0x608010) at ply-event-loop.c:1276 #2 0x0000003727a05da0 in ply_event_loop_run (loop=0x608010) at ply-event-loop.c:1364 #3 0x000000000040369d in main (argc=<value optimized out>, argv=<value optimized out>) at ./plymouth.c:1133 (gdb) =======