msg169276 - (view) |
Author: Aleksey Filippov (sarum9in) |
Date: 2012-08-28 13:03 |
System info:
kernel: 3.4.8-1-ARCH
dist: Arch linux
python: 3.2.3
subprocess.Popen() fails if python interpreter is started with closed 0, 1 or 2 descriptor.
Traceback (most recent call last):
File "<string>", line 14, in <module>
File "/usr/lib/python3.2/subprocess.py", line 745, in __init__
restore_signals, start_new_session)
File "/usr/lib/python3.2/subprocess.py", line 1197, in _execute_child
restore_signals, start_new_session, preexec_fn)
ValueError: errpipe_write must be >= 3
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msg169277 - (view) |
Author: Ezio Melotti (ezio.melotti) * |
Date: 2012-08-28 13:12 |
#10806 seems related.
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msg169344 - (view) |
Author: Ross Lagerwall (rosslagerwall) |
Date: 2012-08-29 06:58 |
It's caused by the following check in _posixsubprocess.c:
if (close_fds && errpipe_write < 3) { /* precondition */
PyErr_SetString(PyExc_ValueError, "errpipe_write must be >= 3");
return NULL;
}
which was written by Gregory P. Smith in 2010 (adding to nosy list).
I'm not entirely sure why this check is here, presumably its due to the way close_fds=True is handled.
The close fds logic is also hardcoded to close fds from 3 upwards,.
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msg169350 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2012-08-29 08:32 |
easy enough to reproduce...
$ ./python.exe -c 'import os, subprocess as s; os.close(0); os.close(1); s.Popen(["/bin/true"])'
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/Users/gps/python/hg/default/Lib/subprocess.py", line 818, in __init__
restore_signals, start_new_session)
File "/Users/gps/python/hg/default/Lib/subprocess.py", line 1363, in _execute_child
restore_signals, start_new_session, preexec_fn)
ValueError: errpipe_write must be >= 3
Examining the code, it looks like that restriction is to prevent the dup2's for any passed in stdin, stdout or stderr pipes from overwriting errpipe_write in Modules/_posixsubprocess.c's child_exec() function.
First guess at a fix: child_exec() needs to detect this situation and dup(errpipe_write) until it gets a fd not in the 0..2 range before the dup2(...) calls that could otherwise blindly clobber it. This could possibly be done by the parent process's _create_pipe() in Lib/subprocess.py when allocating the errpipe_read and errpipe_write fds.
Suggested Workaround: for now for any code running into this (Python daemons launching subprocesses?) - Call os.pipe() twice at the start of your program to burn 4 fds. That'll guarantee 0, 1 and 2 will not be used for this pipe.
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msg169353 - (view) |
Author: Ross Lagerwall (rosslagerwall) |
Date: 2012-08-29 09:20 |
The attached patch + test seems to fix the issue.
It's not very elegant.
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msg169393 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2012-08-29 16:34 |
Yes, something along the lines of that patch is what I was thinking. BTW, this is only necessary for the errpipe_write fd. errpipe_read is for the parent process.
I'm going to do it within _create_pipe so that the optimal _posixsubprocess.cloexec_pipe pipe2() based implementation can be used when possible rather than needing to call _set_cloexec() on the dup'ed fd.
There are some recent Linux specific possibilities such as fcntl with F_DUPFD, or better F_DUPFD_CLOEXEC, that would make this a single call. Using that may be overkill for this situation but it looks easy enough while I'm in there.
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msg169401 - (view) |
Author: Aleksey Filippov (sarum9in) |
Date: 2012-08-29 17:48 |
It may be implemented simplier.
fcntl(fd, F_DUPFD_CLOEXEC, min_fd_number) will allocate new fd at least min_fd_number. So, it is not necessary to do a lot of dup() calls.
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msg169402 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2012-08-29 17:51 |
F_DUPFD_CLOEXEC appears exclusive to modern Linux kernels. Any idea how wide spread support for plain F_DUPFD is? If that is "everywhere" the code I've just whipped up could lose a lot of loops...
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msg169405 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2012-08-29 18:21 |
Here's my initial fix.
If fcntl(errpipe_write, F_DUPFD, 3) is widely available this could be shrunk a bit to avoid the for loop potentially calling dup a few times and tracking the wasted fds to close later.
Otherwise if it isn't I'd rather not bother with F_DUPFD as this code takes the optimal path when F_DUPFD_CLOEXEC is supported (true on all modern linux systems) and should cause no harm beyond a couple extra dup and close syscalls otherwise.
Note: Linux pipe2() support appears in kernels a few revisions after F_DUPFD_CLOEXEC support so the good behavior when pipe2 exists will be kept in this situation as that also means F_DUPFD_CLOEXEC support should exist. The code will work regardless of that (incase someone has a frankenkernel, or other OSes choose to implement one but not the other).
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msg169429 - (view) |
Author: Ross Lagerwall (rosslagerwall) |
Date: 2012-08-30 06:26 |
I sent a review through on rietveld; I'm attaching a patch with the changes so that it compiles and passes the tests.
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msg169447 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2012-08-30 10:36 |
I haven't tested Ross's latest patch, but it looks ok to me.
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msg169449 - (view) |
Author: Richard Oudkerk (sbt) * |
Date: 2012-08-30 11:08 |
Would it simplify matters to stop treating 0,1,2 specially and just add them to pass_fds instead?
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msg204308 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2013-11-25 08:29 |
adding {0,1,2} to fds_to_keep (populated from pass_fds) is indeed an alternate approach. A variant of an alternate patch doing that attached.
This actually simplifies code. Is there anything this would hurt that i'm not seeing?
I suppose it adds minor overhead to the fork_exec() call by passing more in and lookups into the fds_to_keep list now that it will always contain at least 4 values instead of the previous 1. I doubt that is matters (I haven't measured anything).
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msg204879 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2013-12-01 03:04 |
New changeset c4cd891cf167 by Gregory P. Smith in branch '3.3':
Fixes Issue #15798 - subprocess.Popen() no longer fails if file
http://hg.python.org/cpython/rev/c4cd891cf167
New changeset 0387054b2038 by Gregory P. Smith in branch 'default':
Fixes Issue #15798 - subprocess.Popen() no longer fails if file
http://hg.python.org/cpython/rev/0387054b2038
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msg204889 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2013-12-01 08:13 |
New changeset efcdf2a70f2a by Gregory P. Smith in branch '3.3':
Undo supposed fix for Issue #15798 until I understand why this is
http://hg.python.org/cpython/rev/efcdf2a70f2a
New changeset ddbf9632795b by Gregory P. Smith in branch 'default':
Undo supposed fix for Issue #15798 until I understand why this is
http://hg.python.org/cpython/rev/ddbf9632795b
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msg204979 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2013-12-02 00:03 |
New changeset 2df5e1f537b0 by Gregory P. Smith in branch 'default':
Fixes issue #15798: subprocess.Popen() no longer fails if file
http://hg.python.org/cpython/rev/2df5e1f537b0
|
msg204987 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2013-12-02 01:28 |
New changeset 07425df887b5 by Gregory P. Smith in branch '3.3':
Fixes issue #15798: subprocess.Popen() no longer fails if file
http://hg.python.org/cpython/rev/07425df887b5
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msg204990 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2013-12-02 04:02 |
i went with the less invasive in terms of behavior change approach of making sure that the errpipe_write fd is always >= 3. In Python 3.4 the code change was different and much simpler and on the Python only side as all fd's are opened O_CLOEXEC by default.
I'm not entirely sure why the test_multiprocessing_forkserver and test_multiprocessing_spawn failures happened on 3.4 with the earlier change that attempted to always list 0,1,2 in the fds_to_keep (derived from pass_fds) list so there _may_ be a bug lurking elsewhere there but I suspect the bug is actually that we don't always want to blindly list them in fds_to_keep as some programs may have reused some of them for other non-stdio purposes but still want them closed.
The change has been backported to the python-subprocess32 repo.
|
|
Date |
User |
Action |
Args |
2022-04-11 14:57:35 | admin | set | github: 60002 |
2013-12-02 04:02:25 | gregory.p.smith | set | status: open -> closed resolution: fixed messages:
+ msg204990
stage: commit review -> resolved |
2013-12-02 01:28:39 | python-dev | set | messages:
+ msg204987 |
2013-12-02 00:03:43 | python-dev | set | messages:
+ msg204979 |
2013-12-01 08:16:17 | Arfrever | set | nosy:
+ Arfrever
|
2013-12-01 08:14:29 | gregory.p.smith | set | status: closed -> open resolution: fixed -> (no value) stage: resolved -> commit review |
2013-12-01 08:13:45 | python-dev | set | messages:
+ msg204889 |
2013-12-01 03:05:15 | gregory.p.smith | set | status: open -> closed stage: patch review -> resolved resolution: fixed versions:
+ Python 3.4, - Python 3.2 |
2013-12-01 03:04:12 | python-dev | set | nosy:
+ python-dev messages:
+ msg204879
|
2013-11-25 08:29:14 | gregory.p.smith | set | files:
+ issue15798_alternate-pass_fds-gps01.diff
messages:
+ msg204308 |
2013-08-13 22:21:29 | vstinner | set | nosy:
+ vstinner
|
2012-08-30 11:08:02 | sbt | set | nosy:
+ sbt messages:
+ msg169449
|
2012-08-30 10:55:05 | asvetlov | set | nosy:
+ asvetlov
|
2012-08-30 10:36:50 | pitrou | set | messages:
+ msg169447 stage: patch review |
2012-08-30 06:26:58 | rosslagerwall | set | files:
+ issue15798_v2.patch
messages:
+ msg169429 |
2012-08-29 18:21:11 | gregory.p.smith | set | files:
+ issue15798-fix-gps01.diff
messages:
+ msg169405 |
2012-08-29 17:51:48 | gregory.p.smith | set | messages:
+ msg169402 |
2012-08-29 17:48:17 | sarum9in | set | messages:
+ msg169401 |
2012-08-29 16:34:44 | gregory.p.smith | set | messages:
+ msg169393 |
2012-08-29 09:20:16 | rosslagerwall | set | files:
+ issue15798.patch keywords:
+ patch messages:
+ msg169353
|
2012-08-29 08:32:31 | gregory.p.smith | set | assignee: gregory.p.smith messages:
+ msg169350 versions:
+ Python 3.3 |
2012-08-29 08:00:14 | cvrebert | set | nosy:
+ cvrebert
|
2012-08-29 06:58:21 | rosslagerwall | set | nosy:
+ gregory.p.smith messages:
+ msg169344
|
2012-08-28 13:12:44 | ezio.melotti | set | nosy:
+ ezio.melotti, rosslagerwall, pitrou messages:
+ msg169277
components:
+ Library (Lib) type: behavior |
2012-08-28 13:03:49 | sarum9in | create | |