linux-kernel - Re: [PATCH 5.4 086/255] once: add DO_ONCE

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Date:   Tue, 1 Nov 2022 10:03:07 -0700
From:   Oleksandr Tymoshenko <ovt@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Nathan Chancellor <nathan@...nel.org>, christophe.leroy@...roup.eu,
        davem@...emloft.net, edumazet@...gle.com,
        linux-kernel@...r.kernel.org, sashal@...nel.org,
        stable@...r.kernel.org, w@....eu, llvm@...ts.linux.dev
Subject: Re: [PATCH 5.4 086/255] once: add DO_ONCE_SLOW() for sleepable contexts

On Mon, Oct 31, 2022 at 11:25 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Nov 01, 2022 at 05:48:29AM +0100, Greg KH wrote:
> > On Mon, Oct 31, 2022 at 11:27:21AM -0700, Nathan Chancellor wrote:
> > > 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 <c6> 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.
> >
> > I think we should do the latter, fighting with all of the different
> > section entries would be a pain.
> >
> > Unless someone beats me to it, I'll go make up a patch for this...
>
> Can someone test the following patch:

The patch fixes the issue for me, the system boots fine.

>
>
> diff --git a/include/linux/once.h b/include/linux/once.h
> index bb58e1c3aa03..3a6671d961b9 100644
> --- a/include/linux/once.h
> +++ b/include/linux/once.h
> @@ -64,7 +64,7 @@ void __do_once_slow_done(bool *done, struct static_key_true *once_key,
>  #define DO_ONCE_SLOW(func, ...)                                                     \
>         ({                                                                   \
>                 bool ___ret = false;                                         \
> -               static bool __section(".data.once") ___done = false;         \
> +               static bool __section(.data.once) ___done = false;           \
>                 static DEFINE_STATIC_KEY_TRUE(___once_key);                  \
>                 if (static_branch_unlikely(&___once_key)) {                  \
>                         ___ret = __do_once_slow_start(&___done);             \