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If show_mem() is invoked from an Oops or panic context while the crashing CPU or a wedged remote CPU already holds zone->lock, or from an NMI or hardirq context under CONFIG_PREEMPT_RT where spinlock_t is a sleeping rt_mutex, acquiring zone->lock can self-deadlock or fault before post-mortem recovery (such as kdump) can proceed. Check can_spin_trylock() and use spin_trylock_irqsave() when !can_spin_trylock(), in_nmi(), oops_in_progress, or panic_in_progress() is active, and emit the zone header after releasing zone->lock, logging a contention notice and skipping the locked zone rather than spinning indefinitely. Fixes: d999bd9392de ("panic: add options to print system info when panic happens") Signed-off-by: Aaron Tomlin --- mm/show_mem.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/mm/show_mem.c b/mm/show_mem.c index b938cbcd774a..77098077523a 100644 --- a/mm/show_mem.c +++ b/mm/show_mem.c @@ -367,10 +367,17 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask, continue; if (show_mem_node_skip(filter, zone_to_nid(zone), nodemask)) continue; - show_node(zone); - printk(KERN_CONT "%s: ", zone->name); - spin_lock_irqsave(&zone->lock, flags); + if (!can_spin_trylock() || in_nmi() || + oops_in_progress || panic_in_progress()) { + if (!can_spin_trylock() || + !spin_trylock_irqsave(&zone->lock, flags)) { + pr_warn("zone %s lock contended\n", zone->name); + continue; + } + } else { + spin_lock_irqsave(&zone->lock, flags); + } for (order = 0; order < NR_PAGE_ORDERS; order++) { struct free_area *area = &zone->free_area[order]; int type; @@ -385,6 +392,8 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask, } } spin_unlock_irqrestore(&zone->lock, flags); + show_node(zone); + printk(KERN_CONT "%s: ", zone->name); for (order = 0; order < NR_PAGE_ORDERS; order++) { printk(KERN_CONT "%lu*%lukB ", nr[order], K(1UL) << order); -- 2.55.0