Revision 712f3147aee0fbbbbed2da20b21b272c5505125e authored by Linus Torvalds on 13 May 2011, 23:16:41 UTC, committed by Linus Torvalds on 14 May 2011, 17:23:44 UTC
When a register_framebuffer() call results in us removing old conflicting framebuffers, the new registration_lock doesn't protect that situation. And we can't just add the same locking to the function, because these functions call each other: register_framebuffer() calls remove_conflicting_framebuffers, which in turn calls unregister_framebuffer for any conflicting entry. In order to fix it, this just creates wrapper functions around all three functions and makes the versions that actually do the work be called "do_xxx()", leaving just the wrapper that gets the lock and calls the worker function. So the rule becomes simply that "do_xxxx()" has to be called with the lock held, and now do_register_framebuffer() can just call do_remove_conflicting_framebuffers(), and that in turn can call _do_unregister_framebuffer(), and there is no deadlock, and we can hold the registration lock over the whole sequence, fixing the races. It also makes error cases simpler, and fixes one situation where we would return from unregister_framebuffer() without releasing the lock, pointed out by Bruno Prémont. Tested-by: Bruno Prémont <bonbons@linux-vserver.org> Tested-by: Anca Emanuel <anca.emanuel@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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REPORTING-BUGS
[Some of this is taken from Frohwalt Egerer's original linux-kernel FAQ]
What follows is a suggested procedure for reporting Linux bugs. You
aren't obliged to use the bug reporting format, it is provided as a guide
to the kind of information that can be useful to developers - no more.
If the failure includes an "OOPS:" type message in your log or on
screen please read "Documentation/oops-tracing.txt" before posting your
bug report. This explains what you should do with the "Oops" information
to make it useful to the recipient.
Send the output to the maintainer of the kernel area that seems to
be involved with the problem, and cc the relevant mailing list. Don't
worry too much about getting the wrong person. If you are unsure send it
to the person responsible for the code relevant to what you were doing.
If it occurs repeatably try and describe how to recreate it. That is
worth even more than the oops itself. The list of maintainers and
mailing lists is in the MAINTAINERS file in this directory. If you
know the file name that causes the problem you can use the following
command in this directory to find some of the maintainers of that file:
perl scripts/get_maintainer.pl -f <filename>
If it is a security bug, please copy the Security Contact listed
in the MAINTAINERS file. They can help coordinate bugfix and disclosure.
See Documentation/SecurityBugs for more information.
If you are totally stumped as to whom to send the report, send it to
linux-kernel@vger.kernel.org. (For more information on the linux-kernel
mailing list see http://www.tux.org/lkml/).
This is a suggested format for a bug report sent to the Linux kernel mailing
list. Having a standardized bug report form makes it easier for you not to
overlook things, and easier for the developers to find the pieces of
information they're really interested in. Don't feel you have to follow it.
First run the ver_linux script included as scripts/ver_linux, which
reports the version of some important subsystems. Run this script with
the command "sh scripts/ver_linux".
Use that information to fill in all fields of the bug report form, and
post it to the mailing list with a subject of "PROBLEM: <one line
summary from [1.]>" for easy identification by the developers.
[1.] One line summary of the problem:
[2.] Full description of the problem/report:
[3.] Keywords (i.e., modules, networking, kernel):
[4.] Kernel information
[4.1.] Kernel version (from /proc/version):
[4.2.] Kernel .config file:
[5.] Most recent kernel version which did not have the bug:
[6.] Output of Oops.. message (if applicable) with symbolic information
resolved (see Documentation/oops-tracing.txt)
[7.] A small shell script or example program which triggers the
problem (if possible)
[8.] Environment
[8.1.] Software (add the output of the ver_linux script here)
[8.2.] Processor information (from /proc/cpuinfo):
[8.3.] Module information (from /proc/modules):
[8.4.] Loaded driver and hardware information (/proc/ioports, /proc/iomem)
[8.5.] PCI information ('lspci -vvv' as root)
[8.6.] SCSI information (from /proc/scsi/scsi)
[8.7.] Other information that might be relevant to the problem
(please look in /proc and include all information that you
think to be relevant):
[X.] Other notes, patches, fixes, workarounds:
Thank you
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