Bug 971352
| Summary: | strace hangs while tracing parent+child communicating via pipe | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Product: | Red Hat Enterprise Linux 7 | Reporter: | Jan Stancek <jstancek> | ||||||||
| Component: | strace | Assignee: | Jeff Law <law> | ||||||||
| Status: | CLOSED CURRENTRELEASE | QA Contact: | Michael Petlan <mpetlan> | ||||||||
| Severity: | unspecified | Docs Contact: | |||||||||
| Priority: | unspecified | ||||||||||
| Version: | 7.0 | CC: | jarod, jburke, kmcmartin, mpetlan, ohudlick, pfrankli, pkis | ||||||||
| Target Milestone: | beta | ||||||||||
| Target Release: | --- | ||||||||||
| Hardware: | Unspecified | ||||||||||
| OS: | Unspecified | ||||||||||
| Whiteboard: | |||||||||||
| Fixed In Version: | strace-4.8-3.el7 | Doc Type: | Bug Fix | ||||||||
| Doc Text: | Story Points: | --- | |||||||||
| Clone Of: | |||||||||||
| : | 992965 (view as bug list) | Environment: | |||||||||
| Last Closed: | 2014-06-13 10:56:57 UTC | Type: | Bug | ||||||||
| Regression: | --- | Mount Type: | --- | ||||||||
| Documentation: | --- | CRM: | |||||||||
| Verified Versions: | Category: | --- | |||||||||
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||||||
| Cloudforms Team: | --- | Target Upstream Version: | |||||||||
| Embargoed: | |||||||||||
| Bug Depends On: | |||||||||||
| Bug Blocks: | 987469, 992965 | ||||||||||
| Attachments: |
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Created attachment 757606 [details]
strace_hangs.c
Created attachment 760168 [details]
experimental patch v1
With this patch on top of strace-4.7-10.el7.x86_64 I can no longer trigger the hang.
Created attachment 770864 [details]
experimental patch 2 v1 (on top of strace-4.8-2.el7)
One more issue, that caught my eye is that register data is updated in collect_stopped_tcbs() in every iteration of while loop and then same (last) register data is used for all tcbs processed in handle_stopped_tcbs().
Trivial program doing just fork() returned sporadically 0 from clone():
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f3068aeca10) = 0
Jan, That looks like a pretty reasonable change; Denys made a change to when and how strace retrieves the register file. It's pretty obvious that we're using stale data. I'm on the road right now, I'll integrate your patch into rhel7 & dts shortly. Thanks! Tested with strace-4.8-7.el7 and no hang occurred. VERIFIED. This request was resolved in Red Hat Enterprise Linux 7.0. Contact your manager or support representative in case you have further questions about the request. |
Description of problem: "gcc strace_hangs.c; strace -F -tt ./a.out" hangs while tracing 2 processes, which communicate via pipe. (source attached in comment below) 1. hangs on select which is also timed [pid 11039] 06:17:08.751691 <... close resumed> ) = 0 [pid 11038] 06:17:08.751821 <... read resumed> "\0", 1) = 1 [pid 11039] 06:17:08.751849 exit_group(0) = ? [pid 11038] 06:17:08.751932 select(4, [3], NULL, NULL, {4, 994872} <unfinished ...> [pid 11039] 06:17:08.752071 +++ exited with 0 +++ 2. hangs on read from pipe, which has write end closed [pid 11046] 06:18:00.169609 close(4 <unfinished ...> [pid 11045] 06:18:00.169684 select(4, [3], NULL, NULL, {4, 994561} <unfinished ...> [pid 11046] 06:18:00.169737 <... close resumed> ) = 0 [pid 11045] 06:18:00.169802 <... select resumed> ) = 1 (in [3], left {4, 994560}) [pid 11046] 06:18:00.169872 exit_group(0) = ? [pid 11045] 06:18:00.169958 read(3, <unfinished ...> [pid 11046] 06:18:00.170040 +++ exited with 0 +++ Version-Release number of selected component (if applicable): strace-4.7-10.el7.x86_64 3.10.0-0.rc4.59.el7.x86_64 RHEL-7.0-20130529.n.1 How reproducible: 50%, seems to happen more with 1CPU kvm guest Steps to Reproduce: 1. gcc strace_hangs.c 2. strace -F -tt ./a.out Actual results: strace hangs Expected results: strace can complete tracing both parent and child Additional info: I couldn't reproduce it with strace-4.5.19-1.6.el6 on top of RHEL-7.0-20130529.n.1.