summaryrefslogtreecommitdiff
path: root/arch/x86/mm
diff options
context:
space:
mode:
authorRik van Riel <riel@surriel.com>2022-08-05 10:16:44 -0400
committerBorislav Petkov <bp@suse.de>2022-08-24 12:48:05 +0200
commitc926087eb38520b268515ae1a842db6db62554cc (patch)
treeda2a492dc0049efcd7d9a32f3e56bf6f37ef2421 /arch/x86/mm
parent0db7058e8e23e6bbab1b4747ecabd1784c34f50b (diff)
x86/mm: Print likely CPU at segfault time
In a large enough fleet of computers, it is common to have a few bad CPUs. Those can often be identified by seeing that some commonly run kernel code, which runs fine everywhere else, keeps crashing on the same CPU core on one particular bad system. However, the failure modes in CPUs that have gone bad over the years are often oddly specific, and the only bad behavior seen might be segfaults in programs like bash, python, or various system daemons that run fine everywhere else. Add a printk() to show_signal_msg() to print the CPU, core, and socket at segfault time. This is not perfect, since the task might get rescheduled on another CPU between when the fault hit, and when the message is printed, but in practice this has been good enough to help people identify several bad CPU cores. For example: segfault[1349]: segfault at 0 ip 000000000040113a sp 00007ffc6d32e360 error 4 in \ segfault[401000+1000] likely on CPU 0 (core 0, socket 0) This printk can be controlled through /proc/sys/debug/exception-trace. [ bp: Massage a bit, add "likely" to the printed line to denote that the CPU number is not always reliable. ] Signed-off-by: Rik van Riel <riel@surriel.com> Signed-off-by: Borislav Petkov <bp@suse.de> Link: https://lore.kernel.org/r/20220805101644.2e674553@imladris.surriel.com
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/fault.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fa71a5d12e87..a498ae1fbe66 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -769,6 +769,8 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct task_struct *tsk)
{
const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
+ /* This is a racy snapshot, but it's better than nothing. */
+ int cpu = raw_smp_processor_id();
if (!unhandled_signal(tsk, SIGSEGV))
return;
@@ -782,6 +784,14 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
print_vma_addr(KERN_CONT " in ", regs->ip);
+ /*
+ * Dump the likely CPU where the fatal segfault happened.
+ * This can help identify faulty hardware.
+ */
+ printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu,
+ topology_core_id(cpu), topology_physical_package_id(cpu));
+
+
printk(KERN_CONT "\n");
show_opcodes(regs, loglvl);