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In these scenarios, the extracted dmesg buffer (e.g. vmcore-dmesg.txt) is often the sole artefact available for post-mortem triage. Currently, appending supplemental system state (such as memory usage, held locks, active timers, task states, or ftrace buffers) via panic_print prior to kdump requires enabling crash_kexec_post_notifiers. Doing so exposes the crash path to registered panic notifiers (vastly increasing the risk of hanging or deadlocking) and forces panic_print output to be flushed synchronously to physical consoles. On a slow serial console or IPMI Serial-over-LAN (e.g. 115200 baud), flushing comprehensive sys_info() output (e.g. tasks or stacktraces) can exceed 10 seconds, allowing the hardware timer to expire and reset the system before kdump can initialise. Furthermore, on large systems, high-volume telemetry can wrap the printk ring buffer and overwrite the initial Oops, BUG, or panic stack trace. This series introduces the "crash_kexec_in_memory_sys_info" kernel command-line parameter to decouple in-memory telemetry collection from both panic notifiers and physical console flushing when kdump is active: 1. Fixes duplicate and dropped all-CPU backtraces when SYS_INFO_ALL_BT is configured in panic_print across early SMP shutdown and __sys_info(). 2. Avoids spinning indefinitely on zone->lock in show_free_areas() during NMI, Oops, or panic contexts by falling back to non-blocking trylock acquisitions and skipping contended zones. 3. Avoids blocking on timekeeping seqcounts and hrtimer_cpu_base locks in sysrq_timer_list_show() and print_active_timers() during NMI, Oops, or panic contexts. 4. Adds printk console flush suppression across nbcon, legacy consoles, and klogd, alongside ring buffer tail pinning so pre-crash records can still be recycled while protecting the initial crash output from being overwritten by subsequent telemetry or ftrace dumps. 5. Introduces crash_kexec_in_memory_sys_info and invokes panic_in_memory_sys_info() from __crash_kexec() prior to machine_crash_shutdown() when crash_kexec_post_notifiers is not enabled. It also marks the start of crash diagnostics across bust_spinlocks(), __report_bug(), oops_enter(), and vpanic(), and reorders __sys_info() so compact, high-signal dumps (SYS_INFO_MEM, SYS_INFO_LOCKS, SYS_INFO_TIMERS, SYS_INFO_BLOCKED_TASKS) execute before high-volume dumps (SYS_INFO_ALL_BT, SYS_INFO_TASKS, SYS_INFO_FTRACE). Changes since v1: - Split the single patch into a 5-patch series separating prerequisite panic all-CPU backtrace fixes, crash-time lock safety in show_mem() and timer_list, printk/tracing infrastructure, and the crash_kexec integration - Moved in-memory sys_info() collection from vpanic() into __crash_kexec() via panic_in_memory_sys_info() with local interrupts disabled so all crash_kexec() entry points (including direct Oops/die paths prior to vpanic()) are covered, and kept console flush suppression and tail pinning active through machine_crash_shutdown() and machine_kexec() unless machine_kexec() returns - Replaced unconditional ring buffer tail freezing with crash-start sequence pinning (printk_mark_panic_start(), printk_clear_panic_start(), and printk_is_tail_full()), allowing pre-crash records to be recycled while preserving the initial Oops/panic trace, finalising the last record when full, and stopping ftrace_dump_one() before consuming unprinted trace entries - Extended printk_suppress_console_flush() to cover nbcon atomic flushes and kthreads, legacy console_flush_one_record() and kthreads, and wake_up_klogd(), and dropped unnecessary EXPORT_SYMBOL_GPL exports - Added crash-context trylock and NMI-safe timekeeping handling in show_free_areas(), sysrq_timer_list_show(), and print_active_timers(), and fixed duplicate/dropped all-CPU backtraces when SYS_INFO_ALL_BT is used during panic - Link to v1: https://lore.kernel.org/lkml/20260916201546.661384-1-atomlin@atomlin.com/ Aaron Tomlin (5): panic, sys_info: Fix duplicate and dropped all-CPU backtraces in panic mm/show_mem: Avoid blocking on zone->lock during Oops or panic timers: Avoid blocking on hrtimer_cpu_base lock during Oops or panic printk, tracing: Support console flush suppression and tail pinning panic, crash_core, sys_info: Introduce crash_kexec_in_memory_sys_info .../admin-guide/kernel-parameters.txt | 11 ++ include/linux/panic.h | 2 + include/linux/printk.h | 27 +++ include/linux/sched.h | 3 + include/linux/sys_info.h | 4 + kernel/crash_core.c | 6 + kernel/exit.c | 10 ++ kernel/fork.c | 3 + kernel/panic.c | 87 ++++++++- kernel/printk/internal.h | 4 + kernel/printk/nbcon.c | 11 +- kernel/printk/printk.c | 29 ++- kernel/printk/printk_ringbuffer.c | 168 +++++++++++++++++- kernel/time/timer_list.c | 13 +- kernel/trace/trace.c | 20 ++- lib/bug.c | 18 +- lib/bust_spinlocks.c | 22 ++- lib/sys_info.c | 33 ++-- mm/show_mem.c | 15 +- 19 files changed, 447 insertions(+), 39 deletions(-) -- 2.55.0