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panic: add option to dump all CPUs backtraces in panic_print
Currently the "panic_print" parameter/sysctl allows some interesting debug information to be printed during a panic event. This is useful for example in cases the user cannot kdump due to resource limits, or if the user collects panic logs in a serial output (or pstore) and prefers a fast reboot instead of a kdump. Happens that currently there's no way to see all CPUs backtraces in a panic using "panic_print" on architectures that support that. We do have "oops_all_cpu_backtrace" sysctl, but although partially overlapping in the functionality, they are orthogonal in nature: "panic_print" is a panic tuning (and we have panics without oopses, like direct calls to panic() or maybe other paths that don't go through oops_enter() function), and the original purpose of "oops_all_cpu_backtrace" is to provide more information on oopses for cases in which the users desire to continue running the kernel even after an oops, i.e., used in non-panic scenarios. So, we hereby introduce an additional bit for "panic_print" to allow dumping the CPUs backtraces during a panic event. Link: https://lkml.kernel.org/r/20211109202848.610874-3-gpiccoli@igalia.com Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Reviewed-by: Feng Tang <feng.tang@intel.com> Cc: Iurii Zaikin <yzaikin@google.com> Cc: Kees Cook <keescook@chromium.org> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Samuel Iglesias Gonsalvez <siglesias@igalia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -3726,6 +3726,7 @@
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bit 3: print locks info if CONFIG_LOCKDEP is on
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bit 4: print ftrace buffer
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bit 5: print all printk messages in buffer
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bit 6: print all CPUs backtrace (if available in the arch)
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panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
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Format: <hex>[,nousertaint]
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@ -796,6 +796,7 @@ bit 2 print timer info
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bit 3 print locks info if ``CONFIG_LOCKDEP`` is on
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bit 4 print ftrace buffer
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bit 5 print all printk messages in buffer
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bit 6 print all CPUs backtrace (if available in the arch)
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===== ============================================
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So for example to print tasks and memory info on panic, user can::
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@ -66,6 +66,7 @@ EXPORT_SYMBOL_GPL(panic_timeout);
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#define PANIC_PRINT_LOCK_INFO 0x00000008
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#define PANIC_PRINT_FTRACE_INFO 0x00000010
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#define PANIC_PRINT_ALL_PRINTK_MSG 0x00000020
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#define PANIC_PRINT_ALL_CPU_BT 0x00000040
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unsigned long panic_print;
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ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
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@ -152,6 +153,9 @@ static void panic_print_sys_info(void)
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if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
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console_flush_on_panic(CONSOLE_REPLAY_ALL);
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if (panic_print & PANIC_PRINT_ALL_CPU_BT)
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trigger_all_cpu_backtrace();
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if (panic_print & PANIC_PRINT_TASK_INFO)
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show_state();
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