Re: [PATCH 5.4 086/255] once: add DO_ONCE_SLOW() for sleepable contexts

Greg KH
2022-11-01T04:47:40Z

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...

thanks,

greg k-h