Re: [Qemu-devel] [PULL v4 00/35] Misc patches for 2018-12-21

[Paolo Bonzini]

On 04/01/19 14:03, Peter Maydell wrote:
> On Fri, 4 Jan 2019 at 07:59, Paolo Bonzini <address@hidden> wrote:
>> I don't know... I tried running make check under "strace -e fcntl" and I
>> didn't find any occurrences of fcntl(1, O_SETFL, ...|O_NONBLOCK).
> 
> I found this strace command worked to track down some possible
> culprits:
> strace -o /tmp/strace.log -e fcntl,execve,clone -e signal=none -f make
> -C build/x86 V=1 check
> 
> Extracts from the logs:
> 
> 29251 execve("tests/test-char", ["tests/test-char", "-q", "-p",
> "/char/stdio/subprocess", "--GTestSubprocess", "--GTestLogFD", "4"],
> [/* 66 vars */] <unfinished ...>
> 29251 <... execve resumed> )            = 0
> 29251 fcntl(3, F_GETFD)                 = 0
> 29251 fcntl(3, F_SETFD, FD_CLOEXEC)     = 0
> 29251 clone(child_stack=0x7f43946addf0,
> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
> parent_tidptr=0x7f43946ae9d0, tls=0x7f43946ae700,
> child_tidptr=0x7f43946ae9d0) = 29254
> 29251 fcntl(4, F_GETFD)                 = 0
> 29251 fcntl(4, F_SETFD, FD_CLOEXEC)     = 0
> 29251 fcntl(4, F_GETFL)                 = 0x2 (flags O_RDWR)
> 29251 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
> 29251 fcntl(0, F_GETFL)                 = 0x8000 (flags O_RDONLY|O_LARGEFILE)
> 29251 fcntl(0, F_GETFL)                 = 0x8000 (flags O_RDONLY|O_LARGEFILE)
> 29251 fcntl(0, F_SETFL, O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 0
> 29251 fcntl(1, F_GETFL)                 = 0x1 (flags O_WRONLY)
> 29251 fcntl(1, F_SETFL, O_WRONLY|O_NONBLOCK) = 0
> 29251 fcntl(0, F_SETFL, O_RDONLY|O_LARGEFILE) = 0
> 29251 fcntl(0, F_SETFL, O_RDONLY|O_LARGEFILE) = -1 EBADF (Bad file descriptor)
> 29254 +++ exited with 0 +++
> 29251 +++ exited with 0 +++

This one is okay, since the subprocess is using a pipe for stdin and stdout.

QEMU restores O_NONBLOCK at exit (see term_exit in
chardev/char-stdio.c); however, for parallel make and no --output-sync,
a small window does remain where make sees a nonblocking stdout.  Even
that wouldn't explain why the second make inside the while loop always
sees a nonblocking stdout, while the first never does.

Paolo

> (the attempt to F_SETFL a closed stdin is also interesting).
> 
> and
> 
> 30300 execve("tests/hexloader-test", ["tests/hexloader-test",
> "--quiet", "--keep-going", "-m
> =quick", "--GTestLogFD=6"], [/* 68 vars */]) = 0
> 30300 fcntl(3, F_GETFD)                 = 0
> 30300 fcntl(3, F_SETFD, FD_CLOEXEC)     = 0
> 30300 fcntl(4, F_GETFD)                 = 0
> 30300 fcntl(4, F_SETFD, FD_CLOEXEC)     = 0
> 30300 clone(child_stack=0,
> flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
> child_tidptr=0x7f26bdc09a10) = 30301
> 30301 execve("/bin/sh", ["sh", "-c", "exec
> arm-softmmu/qemu-system-arm"...], [/* 69 vars */]) = 0
> 30301 execve("arm-softmmu/qemu-system-arm",
> ["arm-softmmu/qemu-system-arm", "-qtest",
> "unix:/tmp/qtest-30300.sock,nowai"..., "-qtest-log", "/dev/null",
> "-chardev", "socket,path=/tmp/qtest-30300.qmp"..., "-mon",
> "chardev=char0,mode=control", "-machine", "accel=qtest", "-display",
> "none", "-M", "vexpress-a9", "-nographic", ...], [/* 69 vars */]) = 0
> 30301 fcntl(3, F_GETFD)                 = 0
> 30301 fcntl(3, F_SETFD, FD_CLOEXEC)     = 0
> 30301 clone(child_stack=0x7f84f7614730,
> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
> parent_tidptr=0x7f84f76179d0, tls=0x7f84f7617700,
> child_tidptr=0x7f84f76179d0) = 30302
> 30301 fcntl(7, F_GETFD)                 = 0
> 30301 fcntl(7, F_SETFD, FD_CLOEXEC)     = 0
> 30301 fcntl(7, F_GETFL)                 = 0x2 (flags O_RDWR)
> 30301 fcntl(7, F_SETFL, O_RDWR|O_NONBLOCK) = 0
> 30301 fcntl(11, F_GETFL)                = 0x2 (flags O_RDWR)
> 30301 fcntl(11, F_SETFL, O_RDWR|O_NONBLOCK) = 0
> 30301 fcntl(12, F_GETFL)                = 0x2 (flags O_RDWR)
> 30301 fcntl(12, F_SETFL, O_RDWR|O_NONBLOCK) = 0
> 30301 clone(child_stack=0x7f84f6e13730,
> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
> parent_tidptr=0x7f84f6e169d0, tls=0x7f84f6e16700,
> child_tidptr=0x7f84f6e169d0) = 30303
> 30301 fcntl(0, F_GETFL)                 = 0x8000 (flags O_RDONLY|O_LARGEFILE)
> 30301 fcntl(0, F_GETFL)                 = 0x8000 (flags O_RDONLY|O_LARGEFILE)
> 30301 fcntl(0, F_SETFL, O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 0
> 30301 fcntl(1, F_GETFL)                 = 0x8402 (flags
> O_RDWR|O_APPEND|O_LARGEFILE)
> 30301 fcntl(1, F_SETFL, O_RDWR|O_APPEND|O_NONBLOCK|O_LARGEFILE) = 0
> 30301 clone(child_stack=0x7f84f6612730,
> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
> parent_tidptr=0x7f84f66159d0, tls=0x7f84f6615700,
> child_tidptr=0x7f84f66159d0) = 30304
> 30303 +++ exited with 0 +++
> 30301 fcntl(0, F_SETFL, O_RDONLY|O_LARGEFILE) = 0
> 30301 fcntl(0, F_SETFL, O_RDONLY|O_LARGEFILE) = -1 EBADF (Bad file descriptor)
> 30302 +++ exited with 0 +++
> 30301 +++ exited with 0 +++
> 
> where tests/hexloader-test starts a QEMU process which
> makes stdin/stdout non-blocking.
> 
> I didn't try to also track dup/dup2/dup3 use to see whether fd 0/1/2
> were duped to other fds and then set O_NONBLOCK via those, or
> open to see if they were reopened with other contents.
> 
> (Test run is still in-progress, I'll update if there are any more
> interesting bits of logging.)
> 
> thanks
> -- PMM
>