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Subject: Re: [BUG] arm: kgdb: patch_text() in kgdb_arch_set_breakpoint() may sleep
From: Doug Anderson <dianders@chromium.org>
To: Aapo Vienamo <avienamo@nvidia.com>, Kees Cook <keescook@chromium.org>
Cc: nico@linaro.org,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Aapo,

Including the stack trace with this would have been helpful, though
it's not too hard to reproduce.  Here it is:

[  416.510559] BUG: scheduling while atomic: swapper/0/0/0x00010007
[  416.516554] Modules linked in:
[  416.519614] CPU: 0 PID: 0 Comm: swapper/0 Not tainted
4.2.0-rc7-00133-geb63b34 #1073
[  416.527341] Hardware name: Rockchip (Device Tree)
[  416.532042] [<c0017a4c>] (unwind_backtrace) from [<c00133d4>]
(show_stack+0x20/0x24)
[  416.539772] [<c00133d4>] (show_stack) from [<c05400e8>]
(dump_stack+0x84/0xb8)
[  416.546983] [<c05400e8>] (dump_stack) from [<c004913c>]
(__schedule_bug+0x54/0x6c)
[  416.554540] [<c004913c>] (__schedule_bug) from [<c054065c>]
(__schedule+0x80/0x668)
[  416.562183] [<c054065c>] (__schedule) from [<c0540cfc>] (schedule+0xb8/0xd4)
[  416.569219] [<c0540cfc>] (schedule) from [<c0543a3c>]
(schedule_timeout+0x2c/0x234)
[  416.576861] [<c0543a3c>] (schedule_timeout) from [<c05417c0>]
(wait_for_common+0xf4/0x188)
[  416.585109] [<c05417c0>] (wait_for_common) from [<c0541874>]
(wait_for_completion+0x20/0x24)
[  416.593531] [<c0541874>] (wait_for_completion) from [<c00a0104>]
(__stop_cpus+0x58/0x70)
[  416.601608] [<c00a0104>] (__stop_cpus) from [<c00a0580>]
(stop_cpus+0x3c/0x54)
[  416.608817] [<c00a0580>] (stop_cpus) from [<c00a06c4>]
(__stop_machine+0xcc/0xe8)
[  416.616286] [<c00a06c4>] (__stop_machine) from [<c00a0714>]
(stop_machine+0x34/0x44)
[  416.624016] [<c00a0714>] (stop_machine) from [<c00173e8>]
(patch_text+0x28/0x34)
[  416.631399] [<c00173e8>] (patch_text) from [<c001733c>]
(kgdb_arch_set_breakpoint+0x40/0x4c)
[  416.639823] [<c001733c>] (kgdb_arch_set_breakpoint) from
[<c00a0d68>] (kgdb_validate_break_address+0x2c/0x60)
[  416.649719] [<c00a0d68>] (kgdb_validate_break_address) from
[<c00a0e90>] (dbg_set_sw_break+0x1c/0xdc)
[  416.658922] [<c00a0e90>] (dbg_set_sw_break) from [<c00a2e88>]
(gdb_serial_stub+0x9c4/0xba4)
[  416.667259] [<c00a2e88>] (gdb_serial_stub) from [<c00a11cc>]
(kgdb_cpu_enter+0x1f8/0x60c)
[  416.675423] [<c00a11cc>] (kgdb_cpu_enter) from [<c00a18cc>]
(kgdb_handle_exception+0x19c/0x1d0)
[  416.684106] [<c00a18cc>] (kgdb_handle_exception) from [<c0016f7c>]
(kgdb_compiled_brk_fn+0x30/0x3c)
[  416.693135] [<c0016f7c>] (kgdb_compiled_brk_fn) from [<c00091a4>]
(do_undefinstr+0x1a4/0x20c)
[  416.701643] [<c00091a4>] (do_undefinstr) from [<c001400c>]
(__und_svc_finish+0x0/0x34)
[  416.709543] Exception stack(0xc07c1ce8 to 0xc07c1d30)
[  416.714584] 1ce0:                   00000000 c07c6504 c086e290
c086e294 c086e294 c086e290
[  416.722745] 1d00: c07c6504 00000067 00000001 c07c2100 00000027
c07c1d4c c07c1d50 c07c1d30
[  416.730905] 1d20: c00a0990 c00a08d0 60000193 ffffffff
[  416.735947] [<c001400c>] (__und_svc_finish) from [<c00a08d0>]
(kgdb_breakpoint+0x58/0x94)
[  416.744110] [<c00a08d0>] (kgdb_breakpoint) from [<c00a0990>]
(sysrq_handle_dbg+0x58/0x6c)
[  416.752273] [<c00a0990>] (sysrq_handle_dbg) from [<c02c230c>]
(__handle_sysrq+0xac/0x15c)
[  416.760437] [<c02c230c>] (__handle_sysrq) from [<c02c23ec>]
(handle_sysrq+0x30/0x34)


Kees: I think you've dealt with a lot more of these types of issues
than I have.  Any quick thoughts?  If not I can put it on my long-term
list of things to do, but until then we could always just post a
Revert...


-Doug


On Wed, Aug 5, 2015 at 8:50 AM, Aapo Vienamo <avienamo@nvidia.com> wrote:
> Hi,
>
> The breakpoint setting code in arch/arm/kernel/kgdb.c calls
> patch_text(), which ends up trying to sleep while in interrupt context.
> The bug was introduced by commit: 23a4e40 arm: kgdb: Handle read-only
> text / modules. The resulting behavior is "BUG: scheduling while
> atomic..." when setting a breakpoint in kgdb. This was tested on an
> Nvidia Jetson TK1 board with 4.2.0-rc5-next-20150805 kernel.
>
> Regards,
> Aapo Vienamo
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