From: Miroslav Benes <mbenes@suse.cz>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Petr Mladek <pmladek@suse.com>,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
linux-kbuild@vger.kernel.org
Subject: Re: [PATCH v4 00/10] klp-convert livepatch build tooling
Date: Wed, 26 Jun 2019 12:27:11 +0200 (CEST) [thread overview]
Message-ID: <alpine.LSU.2.21.1906261222510.22069@pobox.suse.cz> (raw)
In-Reply-To: <20190625190836.GL20356@redhat.com>
On Tue, 25 Jun 2019, Joe Lawrence wrote:
> On Tue, Jun 25, 2019 at 01:36:37PM +0200, Miroslav Benes wrote:
> >
> > [ ... snip ... ]
> >
> > If I revert commit d59cadc0a8f8 ("[squash] klp-convert: make
> > convert_rela() list-safe") (from Joe's expanded github tree), the problem
> > disappears.
> >
> > I haven't spotted any problem in the code and I cannot explain a
> > dependency on GCC version. Any ideas?
> >
>
> I can confirm that test_klp_convert1.ko crashes with RHEL-7 and its
> older gcc. I added some debugging printf's to klp-convert and see:
>
> % ./scripts/livepatch/klp-convert \
> ./Symbols.list \
> lib/livepatch/test_klp_convert1.klp.o \
> lib/livepatch/test_klp_convert1.ko | \
> grep saved_command_line
>
> convert_rela: oldsec: .rela.text rela @ 0x1279670 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) offset: 0x3
> convert_rela: oldsec: .rela.text rela @ 0x1279cd0 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) offset: 0x9a
> move_rela: rela @ 0x1279670 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) offset: 0x3
> main: skipping rela @ 0x1279cd0 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) (!must_convert)
>
> I think the problem is:
>
> - Relas at different offsets, but for the same symbol may share symbol
> storage. Note the same rela->sym value above.
>
> - Before d59cadc0a8f8 ("[squash] klp-convert: make convert_rela()
> list-safe"), convert_rela() iterated through the entire section's
> relas, moving any of the same name. This was determined not to be
> list safe when moving consecutive relas in the linked list.
>
> - After d59cadc0a8f8 ("[squash] klp-convert: make convert_rela()
> list-safe"), convert_rela() still iterates through the section relas,
> but only updates r1->sym->klp_rela_sec instead of moving them.
> move_rela() was added to be called by the for-each-rela loop in
> main().
>
> - Bug 1: klp_rela_sec probably belongs in struct rela and not struct
> symbol
>
> - Bug 2: the main loop skips over second, third, etc. matching relas
> anyway as the shared symbol name will have already been converted
Yes, it explains the issue.
> The following fix might not be elegant, but I can't think of a clever
> way to handle the original issue d59cadc0a8f8 ("[squash] klp-convert:
> make convert_rela() list-safe") as well as these resulting regressions.
> So I broke out the moving of relas to a seperate loop.
It works. Thanks Joe.
> That is probably
> worth a comment and at the same time we might be able to drop some of
> these other "safe" loop traversals for ordinary list_for_each_entry.
I think _safe from list_for_each_entry_safe(rela, tmprela, &sec->relas,
list) in the main loop could be dropped, because convert_rela() only marks
relas and does not move them anywhere.
Similarly, list_for_each_entry_safe(r1, r2, &oldsec->relas, list) in
convert_rela() itself.
Miroslav
prev parent reply other threads:[~2019-06-26 10:27 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-09 14:38 [PATCH v4 00/10] klp-convert livepatch build tooling Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 01/10] livepatch: Create and include UAPI headers Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 02/10] kbuild: Support for Symbols.list creation Joe Lawrence
2019-05-21 13:48 ` Masahiro Yamada
2019-05-09 14:38 ` [PATCH v4 03/10] livepatch: Add klp-convert tool Joe Lawrence
2019-07-31 2:50 ` Masahiro Yamada
2019-07-31 3:36 ` Masahiro Yamada
2019-08-09 18:42 ` Joe Lawrence
2019-08-13 1:15 ` Masahiro Yamada
2019-05-09 14:38 ` [PATCH v4 04/10] livepatch: Add klp-convert annotation helpers Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 05/10] modpost: Integrate klp-convert Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 06/10] modpost: Add modinfo flag to livepatch modules Joe Lawrence
2019-07-31 5:58 ` Masahiro Yamada
2019-08-12 15:56 ` Joe Lawrence
2019-08-15 15:05 ` Masahiro Yamada
2019-08-16 8:19 ` Miroslav Benes
2019-08-16 12:43 ` Joe Lawrence
2019-08-16 19:01 ` Joe Lawrence
2019-08-19 3:50 ` Masahiro Yamada
2019-08-19 15:55 ` Joe Lawrence
2019-08-20 7:54 ` Miroslav Benes
2019-08-19 3:49 ` Masahiro Yamada
2019-08-19 7:31 ` Miroslav Benes
2019-08-19 16:02 ` Joe Lawrence
2019-08-22 3:35 ` Masahiro Yamada
2019-08-13 10:26 ` Miroslav Benes
2019-05-09 14:38 ` [PATCH v4 07/10] livepatch: Add sample livepatch module Joe Lawrence
2019-08-16 11:35 ` Masahiro Yamada
2019-08-16 12:47 ` Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 08/10] documentation: Update on livepatch elf format Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 09/10] livepatch/selftests: add klp-convert Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 10/10] livepatch/klp-convert: abort on special sections Joe Lawrence
2019-06-13 13:00 ` [PATCH v4 00/10] klp-convert livepatch build tooling Miroslav Benes
2019-06-13 13:15 ` Joe Lawrence
2019-06-13 20:48 ` Joe Lawrence
2019-06-14 8:34 ` Petr Mladek
2019-06-14 14:20 ` Joe Lawrence
2019-06-14 16:36 ` Libor Pechacek
2019-06-25 11:36 ` Miroslav Benes
2019-06-25 13:24 ` Joe Lawrence
2019-06-25 19:08 ` Joe Lawrence
2019-06-26 10:27 ` Miroslav Benes [this message]
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