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authorDoug Anderson <armlinux@m.disordat.com>2015-08-26 18:26:49 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2015-09-16 23:58:46 +0100
commit7ae85dc7687c7e7119053d83d02c560ea217b772 (patch)
tree1663450cdac1b5c0f4a9cdd5a73061d0e5b88d69 /arch/arm/kernel
parent90cde5584a34e210850728bebee4c6fb1a7124ba (diff)
downloadlinux-linaro-stable-7ae85dc7687c7e7119053d83d02c560ea217b772.tar.gz
ARM: 8425/1: kgdb: Don't try to stop the machine when setting breakpoints
In (23a4e40 arm: kgdb: Handle read-only text / modules) we moved to using patch_text() to set breakpoints so that we could handle the case when we had CONFIG_DEBUG_RODATA. That patch used patch_text(). Unfortunately, patch_text() assumes that we're not in atomic context when it runs since it needs to grab a mutex and also wait for other CPUs to stop (which it does with a completion). This would result in a stack crawl if you had CONFIG_DEBUG_ATOMIC_SLEEP and tried to set a breakpoint in kgdb. The crawl looked something like: BUG: scheduling while atomic: swapper/0/0/0x00010007 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.2.0-rc7-00133-geb63b34 #1073 Hardware name: Rockchip (Device Tree) (unwind_backtrace) from [<c00133d4>] (show_stack+0x20/0x24) (show_stack) from [<c05400e8>] (dump_stack+0x84/0xb8) (dump_stack) from [<c004913c>] (__schedule_bug+0x54/0x6c) (__schedule_bug) from [<c054065c>] (__schedule+0x80/0x668) (__schedule) from [<c0540cfc>] (schedule+0xb8/0xd4) (schedule) from [<c0543a3c>] (schedule_timeout+0x2c/0x234) (schedule_timeout) from [<c05417c0>] (wait_for_common+0xf4/0x188) (wait_for_common) from [<c0541874>] (wait_for_completion+0x20/0x24) (wait_for_completion) from [<c00a0104>] (__stop_cpus+0x58/0x70) (__stop_cpus) from [<c00a0580>] (stop_cpus+0x3c/0x54) (stop_cpus) from [<c00a06c4>] (__stop_machine+0xcc/0xe8) (__stop_machine) from [<c00a0714>] (stop_machine+0x34/0x44) (stop_machine) from [<c00173e8>] (patch_text+0x28/0x34) (patch_text) from [<c001733c>] (kgdb_arch_set_breakpoint+0x40/0x4c) (kgdb_arch_set_breakpoint) from [<c00a0d68>] (kgdb_validate_break_address+0x2c/0x60) (kgdb_validate_break_address) from [<c00a0e90>] (dbg_set_sw_break+0x1c/0xdc) (dbg_set_sw_break) from [<c00a2e88>] (gdb_serial_stub+0x9c4/0xba4) (gdb_serial_stub) from [<c00a11cc>] (kgdb_cpu_enter+0x1f8/0x60c) (kgdb_cpu_enter) from [<c00a18cc>] (kgdb_handle_exception+0x19c/0x1d0) (kgdb_handle_exception) from [<c0016f7c>] (kgdb_compiled_brk_fn+0x30/0x3c) (kgdb_compiled_brk_fn) from [<c00091a4>] (do_undefinstr+0x1a4/0x20c) (do_undefinstr) from [<c001400c>] (__und_svc_finish+0x0/0x34) It turns out that when we're in kgdb all the CPUs are stopped anyway so there's no reason we should be calling patch_text(). We can instead directly call __patch_text() which assumes that CPUs have already been stopped. Fixes: 23a4e4050ba9 ("arm: kgdb: Handle read-only text / modules") Reported-by: Aapo Vienamo <avienamo@nvidia.com> Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Stephen Boyd <sboyd@codeaurora.org> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/kernel')
-rw-r--r--arch/arm/kernel/kgdb.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
index a6ad93c9bce3..fd9eefce0a7b 100644
--- a/arch/arm/kernel/kgdb.c
+++ b/arch/arm/kernel/kgdb.c
@@ -259,15 +259,17 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
if (err)
return err;
- patch_text((void *)bpt->bpt_addr,
- *(unsigned int *)arch_kgdb_ops.gdb_bpt_instr);
+ /* Machine is already stopped, so we can use __patch_text() directly */
+ __patch_text((void *)bpt->bpt_addr,
+ *(unsigned int *)arch_kgdb_ops.gdb_bpt_instr);
return err;
}
int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
{
- patch_text((void *)bpt->bpt_addr, *(unsigned int *)bpt->saved_instr);
+ /* Machine is already stopped, so we can use __patch_text() directly */
+ __patch_text((void *)bpt->bpt_addr, *(unsigned int *)bpt->saved_instr);
return 0;
}