Bug 552257
| Summary: | Process-shared futex on a huge page causes livelock | ||||||
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| Product: | [Fedora] Fedora | Reporter: | r6144 <rainy6144> | ||||
| Component: | kernel | Assignee: | Kernel Maintainer List <kernel-maint> | ||||
| Status: | CLOSED WONTFIX | QA Contact: | Fedora Extras Quality Assurance <extras-qa> | ||||
| Severity: | medium | Docs Contact: | |||||
| Priority: | low | ||||||
| Version: | 12 | CC: | anton, dougsland, gansalmon, itamar, kernel-maint | ||||
| Target Milestone: | --- | ||||||
| Target Release: | --- | ||||||
| Hardware: | All | ||||||
| OS: | Linux | ||||||
| Whiteboard: | |||||||
| Fixed In Version: | Doc Type: | Bug Fix | |||||
| Doc Text: | Story Points: | --- | |||||
| Clone Of: | Environment: | ||||||
| Last Closed: | 2010-12-04 00:52:57 UTC | Type: | --- | ||||
| Regression: | --- | Mount Type: | --- | ||||
| Documentation: | --- | CRM: | |||||
| Verified Versions: | Category: | --- | |||||
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||
| Cloudforms Team: | --- | Target Upstream Version: | |||||
| Embargoed: | |||||||
| Attachments: |
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Description
r6144
2010-01-04 14:10:25 UTC
The above test case still fails in kernel-2.6.31.12-174.2.3.fc12.x86_64. Looking at ftrace results with the function graph tracer, it seems that the kernel is stuck in the following loop in get_futex_key():
again:
err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page);
if (err < 0)
return err;
page = compound_head(page);
lock_page(page);
if (!page->mapping) {
unlock_page(page);
put_page(page);
goto again;
}
(I have not bisected the bug, and the following is just my speculation based on a limited understanding of the Linux VM. Please correct me if I'm wrong.)
This looks like a regression introduced in commit 38d47c1b ("futex: rely on get_user_pages() for shared futexes"), which was merged in 2.6.29. Previously get_futex_key() deems a page to be anonymous if it comes from a private mapping, which was reliable but needed mmap_sem. With that patch, page->mapping is used directly. However, anonymous huge pages are created in hugetlb.c:hugetlb_cow(), and their page->mapping is apparently never set, so the above code goes into an infinite loop.
The bug still exists in kernel 2.6.32.11-99.fc12 and libhugetlbfs-2.8-1.fc12. Reported upstream on LKML. Proposed fix: https://patchwork.kernel.org/patch/93525/ Fixed in 2.6.32.12-112 kernel-2.6.32.12-114.fc12 has been submitted as an update for Fedora 12. http://admin.fedoraproject.org/updates/kernel-2.6.32.12-114.fc12 kernel-2.6.32.12-115.fc12 has been submitted as an update for Fedora 12. http://admin.fedoraproject.org/updates/kernel-2.6.32.12-115.fc12 kernel-2.6.32.12-115.fc12 has been pushed to the Fedora 12 stable repository. If problems still persist, please make note of it in this bug report. This message is a reminder that Fedora 12 is nearing its end of life. Approximately 30 (thirty) days from now Fedora will stop maintaining and issuing updates for Fedora 12. It is Fedora's policy to close all bug reports from releases that are no longer maintained. At that time this bug will be closed as WONTFIX if it remains open with a Fedora 'version' of '12'. Package Maintainer: If you wish for this bug to remain open because you plan to fix it in a currently maintained version, simply change the 'version' to a later Fedora version prior to Fedora 12's end of life. Bug Reporter: Thank you for reporting this issue and we are sorry that we may not be able to fix it before Fedora 12 is end of life. If you would still like to see this bug fixed and are able to reproduce it against a later version of Fedora please change the 'version' of this bug to the applicable version. If you are unable to change the version, please add a comment here and someone will do it for you. Although we aim to fix as many bugs as possible during every release's lifetime, sometimes those efforts are overtaken by events. Often a more recent Fedora release includes newer upstream software that fixes bugs or makes them obsolete. The process we are following is described here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping Fedora 12 changed to end-of-life (EOL) status on 2010-12-02. Fedora 12 is no longer maintained, which means that it will not receive any further security or bug fix updates. As a result we are closing this bug. If you can reproduce this bug against a currently maintained version of Fedora please feel free to reopen this bug against that version. Thank you for reporting this bug and we are sorry it could not be fixed. |