• Doug Anderson's avatar
    ARM: 8425/1: kgdb: Don't try to stop the machine when setting breakpoints · 7ae85dc7
    Doug Anderson authored
    In (23a4e405 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-geb63b34b #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: 23a4e405 ("arm: kgdb: Handle read-only text / modules")
    Reported-by: default avatarAapo Vienamo <avienamo@nvidia.com>
    Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
    Reviewed-by: default avatarStephen Boyd <sboyd@codeaurora.org>
    Acked-by: default avatarKees Cook <keescook@chromium.org>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    7ae85dc7
kgdb.c 7.06 KB