dfd5d5bea6
* pinfo.cc (pinfo::init): Reuse shared memory if the state is marked with PID_REAPED. * spawn.cc (child_info_spawn::worker): Don't duplicate myself_pinfo into non-cygwin child. * fork.cc (frok::parent): Improve error output.
156 lines
7.2 KiB
Plaintext
156 lines
7.2 KiB
Plaintext
2012-05-08 cgf-000004
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The change associated with cgf-000003 introduced a new problem.
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Since a handle associated with the parent is no longer being duplicated
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into a non-cygwin "execed child", Windows is free to reuse the pid of
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the parent when the parent exits. However, since we *did* duplicate a
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handle pointing to the pid's shared memory area into the "execed child",
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the shared memory for the pid was still active.
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Since the shared memory was still available, if a new process reuses the
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previous pid, Cygwin would detect that the shared memory was not created
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and had a "PID_REAPED" flag. That was considered an error, and, so, it
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would set procinfo to NULL and pinfo::thisproc would die since this
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situation is not supposed to occur.
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I fixed this in two ways:
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1) If a shared memory region has a PID_REAPED flag then zero it and
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reuse it. This should be safe since you are not really supposed to be
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querying the shared memory region for anything after PID_REAPED has been
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set.
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2) Forego duping a copy of myself_pinfo if we're starting a non-cygwin
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child for exec.
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It seems like 2) is a common theme and an audit of all of the handles
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that are being passed to non-cygwin children is in order for 1.7.16.
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The other minor modification that was made in this change was to add the
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pid of the failing process to fork error output. This helps slightly
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when looking at strace output, even though in this case it was easy to
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find what was failing by looking for '^---' when running the "stv"
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strace dumper. That found the offending exception quickly.
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2012-05-07 cgf-000003
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<1.7.15>
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Don't make Cygwin wait for all children of a non-cygwin child program.
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Fixes: http://cygwin.com/ml/cygwin/2012-05/msg00063.html,
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http://cygwin.com/ml/cygwin/2012-05/msg00075.html
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</1.7.15>
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This problem is due to a recent change which added some robustness and
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speed to Cygwin's exec/spawn handling by not trying to force inheritance
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every time a process is started. See ChangeLog entries starting on
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2012-03-20, and multiple on 2012-03-21.
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Making the handle inheritable meant that, as usual, there were problems
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with non-Cygwin processes. When Cygwin "execs" a non-Cygwin process N,
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all of its N + 1, N + 2, ... children will also inherit the handle.
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That means that Cygwin will wait until all subprocesses have exited
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before it returns.
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I was willing to make this a restriction of starting non-Cygwin
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processes but the problem with allowing that is that it can cause the
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creation of a "limbo" pid when N exits and N + 1 and friends are still
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around. In this scenario, Cygwin dutifully notices that process N has
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died and sets the exit code to indicate that but N's parent will wait on
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rd_proc_pipe and will only return when every N + ... windows process
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has exited.
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The removal of cygheap::pid_handle was not related to the initial
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problem that I set out to fix. The change came from the realization
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that we were duping the current process handle into the child twice and
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only needed to do it once. The current process handle is used by exec
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to keep the Windows pid "alive" so that it will not be reused. So, now
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we just close parent in child_info_spawn::handle_spawn iff we're not
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execing.
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In debugging this it bothered me that 'ps' identified a nonactive pid as
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active. Part of the reason for this was the 'parent' handle in
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child_info was opened in non-Cygwin processes, keeping the pid alive.
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That has been kluged around (more changes after 1.7.15) but that didn't
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fix the problem. On further investigation, this seems to be caused by
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the fact that the shared memory region pid handles were still being
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passed to non-cygwin children, keeping the pid alive in a limbo-like
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fashion. This was easily fixed by having pinfo::init() consider a
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memory region with PID_REAPED as not available. A more robust fix
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should be considered for 1.7.15+ where these handles are not passed
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to non-cygwin processes.
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This fixed the problem where a pid showed up in the list after a user
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does something like: "bash$ cmd /c start notepad" but, for some reason,
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it does not fix the problem where "bash$ setsid cmd /c start notepad".
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That bears investigation after 1.7.15 is released but it is not a
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regression and so is not a blocker for the release.
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2012-05-03 cgf-000002
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<1.7.15>
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Fix problem where too much input was attempted to be read from a
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pty slave. Fixes: http://cygwin.com/ml/cygwin/2012-05/msg00049.html
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</1.7.15>
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My change on 2012/04/05 reintroduced the problem first described by:
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http://cygwin.com/ml/cygwin/2011-10/threads.html#00445
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The problem then was, IIRC, due to the fact that bytes sent to the pty
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pipe were not written as records. Changing pipe to PIPE_TYPE_MESSAGE in
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pipe.cc fixed the problem since writing lines to one side of the pipe
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caused exactly that the number of characters to be read on the other
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even if there were more characters in the pipe.
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To debug this, I first replaced fhandler_tty.cc with the 1.258,
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2012/04/05 version. The test case started working when I did that.
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So, then, I replaced individual functions, one at a time, in
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fhandler_tty.cc with their previous versions. I'd expected this to be a
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problem with fhandler_pty_master::process_slave_output since that had
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seen the most changes but was surprised to see that the culprit was
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fhandler_pty_slave::read().
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The reason was that I really needed the bytes_available() function to
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return the number of bytes which would be read in the next operation
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rather than the number of bytes available in the pipe. That's because
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there may be a number of lines available to be read but the number of
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bytes which will be read by ReadFile should reflect the mode of the pty
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and, if there is a line to read, only the number of bytes in the line
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should be seen as available for the next read.
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Having bytes_available() return the number of bytes which would be read
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seemed to fix the problem but it could subtly change the behavior of
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other callers of this function. However, I actually think this is
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probably a good thing since they probably should have been seeing the
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line behavior.
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2012-05-02 cgf-000001
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<1.7.15>
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Fix problem setting parent pid to 1 when process with children execs
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itself. Fixes: http://cygwin.com/ml/cygwin/2012-05/msg00009.html
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</1.7.15>
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Investigating this problem with strace showed that ssh-agent was
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checking the parent pid and getting a 1 when it shouldn't have. Other
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stuff looked ok so I chose to consider this a smoking gun.
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Going back to the version that the OP said did not have the problem, I
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worked forward until I found where the problem first occurred -
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somewhere around 2012-03-19. And, indeed, the getppid call returned the
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correct value in the working version. That means that this stopped
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working when I redid the way the process pipe was inherited around
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this time period.
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It isn't clear why (and I suspect I may have to debug this further at
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some poit) this hasn't always been a problem but I made the obvious fix.
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We shouldn't have been setting ppid = 1 when we're about to pass off to
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an execed process.
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As I was writing this, I realized that it was necessary to add some
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additional checks. Just checking for "have_execed" isn't enough. If
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we've execed a non-cygwin process then it won't know how to deal with
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any inherited children. So, always set ppid = 1 if we've execed a
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non-cygwin process.
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