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Mon, 31 Oct 2022 11:27:25 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E9CDC61277; Mon, 31 Oct 2022 18:27:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AFB67C433C1; Mon, 31 Oct 2022 18:27:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1667240844; bh=ysU1aPTGfdEz5odAft8BoDlg3O4d2ECMyJRKU6UM7+0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=X+4t9iQNAuMOp5R+kn5W0/iDMkNQ7Q5pAytUREOILT9TWByk3Iqsvlm9EApkzvKEF iz+0wfKJxETwZqiD1H9pGsBFaGrhZRl0g0aiL8zNZ5apLzLUexGpj7hjHgOutB1wvk AQc0Q6txql3vRJn7sITC0HeJMWcDV+nCL756jxvi2l0hJ/Tk/MwQe+A/rnShiutJSB CA9sRmRmQF9iAur4Y//KwrooT10Hg5YdVTwA/YlcAVcx+Q2Dfg/1l1O72uVntgxynw KuMlbMNyFHNtxbA8qSKKu7onaNIlLyIyPpTNc8H9Uk75UNO9uHWEZDVoBCGfVJy/NA vy3GckwVtzpjQ== Date: Mon, 31 Oct 2022 11:27:21 -0700 From: Nathan Chancellor To: Oleksandr Tymoshenko Cc: gregkh@linuxfoundation.org, christophe.leroy@csgroup.eu, davem@davemloft.net, edumazet@google.com, linux-kernel@vger.kernel.org, sashal@kernel.org, stable@vger.kernel.org, w@1wt.eu, llvm@lists.linux.dev Subject: Re: [PATCH 5.4 086/255] once: add DO_ONCE_SLOW() for sleepable contexts Message-ID: References: <20221024113005.376059449@linuxfoundation.org> <20221029011211.4049810-1-ovt@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221029011211.4049810-1-ovt@google.com> X-Spam-Status: No, score=-8.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Oleksandr, On Sat, Oct 29, 2022 at 01:12:11AM +0000, Oleksandr Tymoshenko wrote: > Hello, > > This commit causes the following panic in kernel built with clang > (GCC build is not affected): > > [ 8.320308] BUG: unable to handle page fault for address: ffffffff97216c6a [26/4066] > [ 8.330029] #PF: supervisor write access in kernel mode > [ 8.337263] #PF: error_code(0x0003) - permissions violation > [ 8.344816] PGD 12e816067 P4D 12e816067 PUD 12e817063 PMD 800000012e2001e1 > [ 8.354337] Oops: 0003 [#1] SMP PTI > [ 8.359178] CPU: 2 PID: 437 Comm: curl Not tainted 5.4.220 #15 > [ 8.367241] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 > [ 8.378529] RIP: 0010:__do_once_slow_done+0xf/0xa0 > [ 8.384962] Code: 1b 84 db 74 0c 48 c7 c7 80 ce 8d 97 e8 fa e9 4a 00 84 db 0f 94 c0 5b 5d c3 66 90 55 48 89 e5 41 57 41 56 > 53 49 89 d7 49 89 f6 07 01 48 c7 c7 80 ce 8d 97 e8 d2 e9 4a 00 48 8b 3d 9b de c9 00 > [ 8.409066] RSP: 0018:ffffb764c02d3c90 EFLAGS: 00010246 > [ 8.415697] RAX: 4f51d3d06bc94000 RBX: d474b86ddf7162eb RCX: 000000007229b1d6 > [ 8.424805] RDX: 0000000000000000 RSI: ffffffff9791b4a0 RDI: ffffffff97216c6a > [ 8.434108] RBP: ffffb764c02d3ca8 R08: 0e81c130f1159fc1 R09: 1d19d60ce0b52c77 > [ 8.443408] R10: 8ea59218e6892b1f R11: d5260237a3c1e35c R12: ffff9c3dadd42600 > [ 8.452468] R13: ffffffff97910f80 R14: ffffffff9791b4a0 R15: 0000000000000000 > [ 8.461416] FS: 00007eff855b40c0(0000) GS:ffff9c3db7a80000(0000) knlGS:0000000000000000 > [ 8.471632] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 8.478763] CR2: ffffffff97216c6a CR3: 000000022ded0000 CR4: 00000000000006a0 > [ 8.487789] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 8.496684] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 8.505443] Call Trace: > [ 8.508568] __inet_hash_connect+0x523/0x530 > [ 8.513839] ? inet_hash_connect+0x50/0x50 > [ 8.518818] ? secure_ipv4_port_ephemeral+0x69/0xe0 > [ 8.525003] tcp_v4_connect+0x2c5/0x410 > [ 8.529858] __inet_stream_connect+0xd7/0x360 > [ 8.535329] ? _raw_spin_unlock+0xe/0x10 > ... skipped ... > > > The root cause is the difference in __section macro semantics between 5.4 and > later LTS releases. On 5.4 it stringifies the argument so the ___done > symbol is created in a bogus section ".data.once", with double quotes: > > % readelf -S vmlinux | grep data.once > [ 5] ".data.once" PROGBITS ffffffff82216c6a 01416c6a Thanks for the report! The reason this does not happen in mainline is due to commit 33def8498fdd ("treewide: Convert macro and uses of __section(foo) to __section("foo")"), which came as a result of these issues: https://github.com/ClangBuiltLinux/linux/issues/619 https://llvm.org/pr42950 To keep stable from diverging, it would probably be best to pick 33def8498fdd and fight through whatever conflicts there are. If that is not a suitable solution, the next best thing would be to remove the quotes like was done in commit bfafddd8de42 ("include/linux/compiler.h: fix Oops for Clang-compiled kernels") for all instances of __section(...) or __attribute__((__section__(...))), which should resolve the specific problem you are seeing. In the future, please feel free to cc issues that you see with clang to llvm@lists.linux.dev so that we can chime in sooner :) Cheers, Nathan