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Message-Id: <200806180026.27247.m.kozlowski@tuxland.pl> Date: Wed, 18 Jun 2008 00:26:27 +0200 From: Mariusz Kozlowski <m.kozlowski@...land.pl> To: Peter 1 Oberparleiter <Peter.Oberparleiter@...ibm.com> Cc: linux-mm@...ck.org, balbir@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: 2.6.26-rc5-mm1 Hello, > Andrew Morton <akpm@...ux-foundation.org> wrote on 10.06.2008 07:01:49: > > On Tue, 10 Jun 2008 06:57:02 +0200 Mariusz Kozlowski <m. > > kozlowski@...land.pl> wrote: > > > > > Witam, > > > > > > > On Mon, 9 Jun 2008 21:14:54 +0200 > > > > Mariusz Kozlowski <m.kozlowski@...land.pl> wrote: > > > > > > > > > Hello Balbir, > > > > > > > > > > > Andrew Morton wrote: > > > > > > > Temporarily at > > > > > > > > > > > > > > http://userweb.kernel.org/~akpm/2.6.26-rc5-mm1/ > > > > > > > > > > > > > > > > > > > I've hit a segfault, the last few lines on my console are > > > > > > > > > > > > > > > > > > Testing -fstack-protector-all feature > > > > > > registered taskstats version 1 > > > > > > debug: unmapping init memory ffffffff80c03000..ffffffff80dd8000 > > > > > > init[1]: segfault at 7fff701fe880 ip 7fff701fee5e sp > > 7fff7006e6d0 error 7 > > > > > > > > > > > > With absolutely no stack trace. I'll dig deeper. > > > > > > > > > > Hey, I see something similar and I actually have a stack > > trace. Here it goes: > > > > > > > > > > bash[498] segfault at ffffffff80868b58 ip ffffffffff600412 sp > > 7fffa3d010f0 error 7 > > > > > init[1] segfault at ffffffff80868b58 ip ffffffffff600412 sp > > 7fff9e97f640 error 7 > > > > > init[1] segfault at ffffffff80868b58 ip ffffffffff600412 sp > > 7fff9e97eed0 error 7 > > > > > Kernel panic - not syncing: Attemted to kill init! > > > > > Pid 1, comm: init Not tainted 2.6.26-rc5-mm1 #1 > > > > > > > > > > Call Trace: > > > > > [<ffffffff80254632>] panic+0xe2/0x260 > > > > > [<ffffffff802fa8ba>] ? __slab_free+0x10a/0x630 > > > > > [<ffffffff80265a8e>] ? __sigqueue_free+0x5e/0x70 > > > > > [<ffffffff802851eb>] ? trace_hardirqs_off+0x1b/0x30 > > > > > [<ffffffff802851eb>] ? trace_hardirqs_off+0x1b/0x30 > > > > > [<ffffffff80259b54>] do_exit+0xb84/0xc30 > > > > > [<ffffffff80259c5a>] do_group_exit+0x5a/0x110 > > > > > [<ffffffff8026a3b5>] get_signal_to_deliver+0x2c5/0x620 > > > > > [<ffffffff8020bb3b>] do_notify_resume+0x11b/0xd10 > > > > > [<ffffffff8028da5b>] ? trace_hardirqs_on+0x1b/0x30 > > > > > [<ffffffff805cd0f3>] ? _spin_unlock_irqrestore+0x93/0x130 > > > > > [<ffffffff8026865c>] ? force_sig_info+0x10c/0x130 > > > > > [<ffffffff8022fb9c>] ? force_sig_info_fault+0x2c/0x40 > > > > > [<ffffffff802dd7dd>] ? print_vma_addr+0x10d/0x1d0 > > > > > [<ffffffff805cbb67>] ? trace_hardirqs_on_thunk+0x3a/0x3f > > > > > [<ffffffff8028d8da>] ? trace_hardirqs_on_caller+0x15a/0x2c0 > > > > > [<ffffffff8020d4c9>] retint_signal+0x46/0x8d > > > > > > > > > > This was copied manually so typos are possible. > > > > > > > > > > > > > Thanks. Could someone send a config please? Or a bisection result > ;) > > > > > > In my case it turns out to be gcov patches - in which I'm interested > > > in to see (and play with) the tests coverage. > > > > > > # > > > # gcov > > > # > > > kernel-call-constructors.patch > > > kernel-introduce-gcc_version_lower-macro.patch > > > seq_file-add-function-to-write-binary-data.patch > > > GOOD > > > gcov-add-gcov-profiling-infrastructure.patch > > > GOOD > > > gcov-create-links-to-gcda-files-in-build-directory.patch > > > gcov-architecture-specific-compile-flag-adjustments.patch > > > BAD > > > > > > I can not bisect between the last two due to build error. Config > > is attached. > > > > > > > (cc Peter) Sorry for the delay. Unfortunately I don't have as much time for this as I'd like to. > Thanks for the report. These look like the "known architecture problems" > that I've hinted at in the gcov announcement post (I'm assuming this is > x86_64 as I've seem similar reports in the past). > > Possible reasons: > > 1) initrd overwrites kernel: When kernel and initrd are loaded to static > addresses, the oversized gcov kernel may overlap with the initrd load > address. Solution: move initrd loading address. Not using initrd. > 2) out-of-memory: Kernel plus profiling code may just not fit into a > minimal memory configuration any more. Solution: add memory. 2G is ok I assume. > 3) write-protection of kernel code: gcc keeps profiling code and data > close together in the .text section. Solution: any mechanism that > protects .text against writes should be disabled when running a > profiled kernel. Not using it. > 4) as of yet undiscovered incompatibilities between arch-dependent code > and gcc's -fprofile-arcs option. Examples would be: > > * code which is run before memory access preparations were made > * hard coded section sizes > * relative address displacements which are out of range > > Unfortunately I neither have access to a machine nor the skill to debug > 4) myself, so if 1)-3) can be ruled out, Yes they can be ruled out. > I'd like to ask for more help > on this one: > > First off, someone needs to track down the offending file(s). This is > done by putting a line containing "GCOV := n" in all Makefiles below > arch/x86_64 (or go one step further back and set > CONFIG_GCOV_PROFILE_ALL=n). If my assumption is correct, then the > kernel should boot fine afterwards. In that case, remove the lines > again one-by-one, while compiling and booting after each change. If the > problem can be narrowed down to a single Makefile, replace the single > "GCOV := n" line with multiple "GCOV_file.o := n" lines, one for each > generated object file. Then again, same approach as before: remove > those lines, compile and boot until it breaks. Finally post your > results. After a few hours and tons of reboots I narrowed it down to arch/x86/kernel/Makefile: a) works obj-y += tsc_$(BITS).o io_delay.o rtc.o GCOV_tsc_$(BITS).o := n #GCOV_io_delay.o := n #GCOV_rtc.o := n b) doesn't work obj-y += tsc_$(BITS).o io_delay.o rtc.o #GCOV_tsc_$(BITS).o := n #GCOV_io_delay.o := n #GCOV_rtc.o := n and that points to arch/x86/kernel/tsc_64.c > At this point we would need someone with x86_64 arch skills to look at > the file and find out why this code is broken with "-fprofile-arcs" > enabled (on s390 we discovered at least one actual code bug this way, > so the analysis might just be of general use). Alternatively we can > just keep these files from being profiled. 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