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Commit 82202b6f authored by Isaac J. Manjarres's avatar Isaac J. Manjarres
Browse files

mm/memory_hotplug: Fix deadlock in try_online_one_block() 



There is a possible scenario where the system can deadlock
itself when it is low on memory, and attempts to online
a memory block. Consider the following scenario:

 -A thread in userspace onlines a memory block through sysfs-
 state_store() /* Acquires the device_hotplug_lock */
 device_online()
 memory_subsys_online()
 memory_block_change_state()
 memory_block_action()
 online_pages()
 memory_notify(MEM_GOING_ONLINE, ...)
 online_page_ext()
 alloc_page_ext()
 __alloc_pages_nodemask(GFP_KERNEL, ...)
 /* System enters into a critically low memory state */
 out_of_memory()
 try_online_one_block() /* Invokes lock_device_hotplug() and deadlocks */

Fix deadlock by introducing and using trylock_device_hotplug()
instead of lock_device_hotplug().

Change-Id: I52bc8075ae713c50e3c381216f3616ce8366cf31
Signed-off-by: default avatarIsaac J. Manjarres <isaacm@codeaurora.org>
parent c322899f

drivers/base/core.c

+5 −0
Original line number Diff line number Diff line
@@ -1321,6 +1321,11 @@ int lock_device_hotplug_sysfs(void) 
	return restart_syscall();

}



int trylock_device_hotplug(void)

{

	return mutex_trylock(&device_hotplug_lock);

}



#ifdef CONFIG_SCHED_WALT

void lock_device_hotplug_assert(void)

{

include/linux/device.h

+1 −0
Original line number Diff line number Diff line
@@ -1592,6 +1592,7 @@ static inline bool device_supports_offline(struct device *dev) 
extern void lock_device_hotplug(void);

extern void unlock_device_hotplug(void);

extern int lock_device_hotplug_sysfs(void);

extern int trylock_device_hotplug(void);

#ifdef CONFIG_SCHED_WALT

extern void lock_device_hotplug_assert(void);

#endif

mm/memory_hotplug.c

+2 −1
Original line number Diff line number Diff line
@@ -1025,7 +1025,8 @@ bool try_online_one_block(int nid) 
	unsigned long zone_start, zone_size;

	bool onlined_block = false;



	lock_device_hotplug();

	if (!trylock_device_hotplug())

		return false;



	zone_start = PFN_PHYS(zone->zone_start_pfn);

	zone_size = zone->spanned_pages << PAGE_SHIFT;