kernel/linux.git/lib/nmi_backtrace.c, branch v6.12.80

nmi_backtrace: allow excluding an arbitrary CPU

2023-08-18T17:19:00+00:00

The APIs that allow backtracing across CPUs have always had a way to exclude the current CPU. This convenience means callers didn't need to find a place to allocate a CPU mask just to handle the common case. Let's extend the API to take a CPU ID to exclude instead of just a boolean. This isn't any more complex for the API to handle and allows the hardlockup detector to exclude a different CPU (the one it already did a trace for) without needing to find space for a CPU mask. Arguably, this new API also encourages safer behavior. Specifically if the caller wants to avoid tracing the current CPU (maybe because they already traced the current CPU) this makes it more obvious to the caller that they need to make sure that the current CPU ID can't change. [akpm@linux-foundation.org: fix trigger_allbutcpu_cpu_backtrace() stub] Link: https://lkml.kernel.org/r/20230804065935.v4.1.Ia35521b91fc781368945161d7b28538f9996c182@changeid Signed-off-by: Douglas Anderson Acked-by: Michal Hocko Cc: kernel test robot Cc: Lecopzer Chen Cc: Petr Mladek Cc: Pingfan Liu Signed-off-by: Andrew Morton

x86/nmi: Print reasons why backtrace NMIs are ignored

2023-01-19T23:55:12+00:00

Instrument nmi_trigger_cpumask_backtrace() to dump out diagnostics based on evidence accumulated by exc_nmi(). These diagnostics are dumped for CPUs that ignored an NMI backtrace request for more than 10 seconds. [ paulmck: Apply Ingo Molnar feedback. ] Signed-off-by: Paul E. McKenney Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Reviewed-by: Ingo Molnar

printk: rename cpulock functions

2022-04-22T19:30:57+00:00

Since the printk cpulock is CPU-reentrant and since it is used in all contexts, its usage must be carefully considered and most likely will require programming locklessly. To avoid mistaking the printk cpulock as a typical lock, rename it to cpu_sync. The main functions then become: printk_cpu_sync_get_irqsave(flags); printk_cpu_sync_put_irqrestore(flags); Add extra notes of caution in the function description to help developers understand the requirements for correct usage. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20220421212250.565456-2-john.ogness@linutronix.de

printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces

2021-11-10T15:12:00+00:00

printk from NMI context relies on irq work being raised on the local CPU to print to console. This can be a problem if the NMI was raised by a lockup detector to print lockup stack and regs, because the CPU may not enable irqs (because it is locked up). Introduce printk_trigger_flush() that can be called another CPU to try to get those messages to the console, call that where printk_safe_flush was previously called. Fixes: 93d102f094be ("printk: remove safe buffers") Cc: stable@vger.kernel.org # 5.15 Signed-off-by: Nicholas Piggin Reviewed-by: Petr Mladek Reviewed-by: John Ogness Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20211107045116.1754411-1-npiggin@gmail.com

lib/nmi_backtrace: Serialize even messages about idle CPUs

2021-07-30T07:25:34+00:00

The commit 55d6af1d66885059ffc2a ("lib/nmi_backtrace: explicitly serialize banner and regs") serialized backtraces from more CPUs using the re-entrant printk_printk_cpu lock. It was a preparation step for removing the obsolete nmi_safe buffers. The single-line messages about idle CPUs were not serialized against other CPUs and might appear in the middle of backtrace from another CPU, for example: [56394.590068] NMI backtrace for cpu 2 [56394.590069] CPU: 2 PID: 444 Comm: systemd-journal Not tainted 5.14.0-rc1-default+ #268 [56394.590071] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 [56394.590072] RIP: 0010:lock_is_held_type+0x0/0x120 [56394.590071] NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xb/0x10 [56394.590076] Code: a2 38 ff 0f 0b 8b 44 24 04 eb bd 48 8d ... [56394.590077] RSP: 0018:ffffab02c07c7e68 EFLAGS: 00000246 [56394.590079] RAX: 0000000000000000 RBX: ffff9a7bc0ec8a40 RCX: ffffffffaab8eb40 It might cause confusion what CPU the following lines belongs to and whether the backtraces are really serialized. Prevent the confusion and serialize also the single line message against other CPUs. Fixes: 55d6af1d66885059ffc2a ("lib/nmi_backtrace: explicitly serialize banner and regs") Reviewed-by: John Ogness Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210727080939.27193-1-pmladek@suse.com

printk: remove safe buffers

2021-07-26T13:09:34+00:00

With @logbuf_lock removed, the high level printk functions for storing messages are lockless. Messages can be stored from any context, so there is no need for the NMI and safe buffers anymore. Remove the NMI and safe buffers. Although the safe buffers are removed, the NMI and safe context tracking is still in place. In these contexts, store the message immediately but still use irq_work to defer the console printing. Since printk recursion tracking is in place, safe context tracking for most of printk is not needed. Remove it. Only safe context tracking relating to the console and console_owner locks is left in place. This is because the console and console_owner locks are needed for the actual printing. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-4-john.ogness@linutronix.de

lib/nmi_backtrace: explicitly serialize banner and regs

2021-07-26T13:07:15+00:00

Currently the nmi_backtrace is serialized against other CPUs because the messages are sent to the NMI buffers. Once these buffers are removed, only the dumped stack will be serialized against other CPUs (via the printk_cpu_lock). Also serialize the nmi_backtrace banner and regs using the printk_cpu_lock so that per-CPU serialization will be preserved even after the NMI buffers are removed. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-2-john.ogness@linutronix.de

lib: Add backtrace_idle parameter to force backtrace of idle CPUs

2020-08-24T21:24:25+00:00

Currently, the nmi_cpu_backtrace() declines to produce backtraces for idle CPUs. This is a good choice in the common case in which problems are caused only by non-idle CPUs. However, there are occasionally situations in which idle CPUs are helping to cause problems. This commit therefore adds an nmi_backtrace.backtrace_idle kernel boot parameter that causes nmi_cpu_backtrace() to dump stacks even of idle CPUs. Signed-off-by: Paul E. McKenney Cc: Jonathan Corbet Cc: Thomas Gleixner Cc: Andrew Morton Cc: Greg Kroah-Hartman Cc:

printk/nmi: Prevent deadlock when accessing the main log buffer in NMI

2018-07-09T12:10:40+00:00

The commit 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI when logbuf_lock is available") brought back the possible deadlocks in printk() and NMI. The check of logbuf_lock is done only in printk_nmi_enter() to prevent mixed output. But another CPU might take the lock later, enter NMI, and: + Both NMIs might be serialized by yet another lock, for example, the one in nmi_cpu_backtrace(). + The other CPU might get stopped in NMI, see smp_send_stop() in panic(). The only safe solution is to use trylock when storing the message into the main log-buffer. It might cause reordering when some lines go to the main lock buffer directly and others are delayed via the per-CPU buffer. It means that it is not useful in general. This patch replaces the problematic NMI deferred context with NMI direct context. It can be used to mark a code that might produce many messages in NMI and the risk of losing them is more critical than problems with eventual reordering. The context is then used when dumping trace buffers on oops. It was the primary motivation for the original fix. Also the reordering is even smaller issue there because some traces have their own time stamps. Finally, nmi_cpu_backtrace() need not longer be serialized because it will always us the per-CPU buffers again. Fixes: 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI when logbuf_lock is available") Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20180627142028.11259-1-pmladek@suse.com To: Steven Rostedt Cc: Peter Zijlstra Cc: Tetsuo Handa Cc: Sergey Senozhatsky Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

lib/nmi_backtrace.c: fix kernel text address leak

2017-11-18T00:10:02+00:00

Don't leak idle function address in NMI backtrace. Link: http://lkml.kernel.org/r/20171106165648.GA95243@sofia Signed-off-by: Liu Changcheng Reviewed-by: Petr Mladek Reviewed-by: Josh Poimboeuf Reviewed-by: Sergey Senozhatsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds