linux/mm/swap_slots.c
Huang Ying 093b995e3b mm, swap: Remove WARN_ON_ONCE() in free_swap_slot()
Before commit 452b94b8c8 ("mm/swap: don't BUG_ON() due to
uninitialized swap slot cache"), the following bug is reported,

  ------------[ cut here ]------------
  kernel BUG at mm/swap_slots.c:270!
  invalid opcode: 0000 [#1] SMP
  CPU: 5 PID: 1745 Comm: (sd-pam) Not tainted 4.11.0-rc1-00243-g24c534bb161b #1
  Hardware name: System manufacturer System Product Name/Z170-K, BIOS 1803 05/06/2016
  RIP: 0010:free_swap_slot+0xba/0xd0
  Call Trace:
   swap_free+0x36/0x40
   do_swap_page+0x360/0x6d0
   __handle_mm_fault+0x880/0x1080
   handle_mm_fault+0xd0/0x240
   __do_page_fault+0x232/0x4d0
   do_page_fault+0x20/0x70
   page_fault+0x22/0x30
  ---[ end trace aefc9ede53e0ab21 ]---

This is raised by the BUG_ON(!swap_slot_cache_initialized) in
free_swap_slot().  This is incorrect, because even if the swap slots
cache fails to be initialized, the swap should operate properly without
the swap slots cache.  And the use_swap_slot_cache check later in the
function will protect the uninitialized swap slots cache case.

In commit 452b94b8c8, the BUG_ON() is replaced by WARN_ON_ONCE().  In
the patch, the WARN_ON_ONCE() is removed too.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-03-21 14:13:19 -07:00

341 lines
8.8 KiB
C

/*
* Manage cache of swap slots to be used for and returned from
* swap.
*
* Copyright(c) 2016 Intel Corporation.
*
* Author: Tim Chen <tim.c.chen@linux.intel.com>
*
* We allocate the swap slots from the global pool and put
* it into local per cpu caches. This has the advantage
* of no needing to acquire the swap_info lock every time
* we need a new slot.
*
* There is also opportunity to simply return the slot
* to local caches without needing to acquire swap_info
* lock. We do not reuse the returned slots directly but
* move them back to the global pool in a batch. This
* allows the slots to coaellesce and reduce fragmentation.
*
* The swap entry allocated is marked with SWAP_HAS_CACHE
* flag in map_count that prevents it from being allocated
* again from the global pool.
*
* The swap slots cache is protected by a mutex instead of
* a spin lock as when we search for slots with scan_swap_map,
* we can possibly sleep.
*/
#include <linux/swap_slots.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/vmalloc.h>
#include <linux/mutex.h>
#ifdef CONFIG_SWAP
static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
static bool swap_slot_cache_active;
bool swap_slot_cache_enabled;
static bool swap_slot_cache_initialized;
DEFINE_MUTEX(swap_slots_cache_mutex);
/* Serialize swap slots cache enable/disable operations */
DEFINE_MUTEX(swap_slots_cache_enable_mutex);
static void __drain_swap_slots_cache(unsigned int type);
static void deactivate_swap_slots_cache(void);
static void reactivate_swap_slots_cache(void);
#define use_swap_slot_cache (swap_slot_cache_active && \
swap_slot_cache_enabled && swap_slot_cache_initialized)
#define SLOTS_CACHE 0x1
#define SLOTS_CACHE_RET 0x2
static void deactivate_swap_slots_cache(void)
{
mutex_lock(&swap_slots_cache_mutex);
swap_slot_cache_active = false;
__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
mutex_unlock(&swap_slots_cache_mutex);
}
static void reactivate_swap_slots_cache(void)
{
mutex_lock(&swap_slots_cache_mutex);
swap_slot_cache_active = true;
mutex_unlock(&swap_slots_cache_mutex);
}
/* Must not be called with cpu hot plug lock */
void disable_swap_slots_cache_lock(void)
{
mutex_lock(&swap_slots_cache_enable_mutex);
swap_slot_cache_enabled = false;
if (swap_slot_cache_initialized) {
/* serialize with cpu hotplug operations */
get_online_cpus();
__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
put_online_cpus();
}
}
static void __reenable_swap_slots_cache(void)
{
swap_slot_cache_enabled = has_usable_swap();
}
void reenable_swap_slots_cache_unlock(void)
{
__reenable_swap_slots_cache();
mutex_unlock(&swap_slots_cache_enable_mutex);
}
static bool check_cache_active(void)
{
long pages;
if (!swap_slot_cache_enabled || !swap_slot_cache_initialized)
return false;
pages = get_nr_swap_pages();
if (!swap_slot_cache_active) {
if (pages > num_online_cpus() *
THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
reactivate_swap_slots_cache();
goto out;
}
/* if global pool of slot caches too low, deactivate cache */
if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
deactivate_swap_slots_cache();
out:
return swap_slot_cache_active;
}
static int alloc_swap_slot_cache(unsigned int cpu)
{
struct swap_slots_cache *cache;
swp_entry_t *slots, *slots_ret;
/*
* Do allocation outside swap_slots_cache_mutex
* as vzalloc could trigger reclaim and get_swap_page,
* which can lock swap_slots_cache_mutex.
*/
slots = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
if (!slots)
return -ENOMEM;
slots_ret = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
if (!slots_ret) {
vfree(slots);
return -ENOMEM;
}
mutex_lock(&swap_slots_cache_mutex);
cache = &per_cpu(swp_slots, cpu);
if (cache->slots || cache->slots_ret)
/* cache already allocated */
goto out;
if (!cache->lock_initialized) {
mutex_init(&cache->alloc_lock);
spin_lock_init(&cache->free_lock);
cache->lock_initialized = true;
}
cache->nr = 0;
cache->cur = 0;
cache->n_ret = 0;
cache->slots = slots;
slots = NULL;
cache->slots_ret = slots_ret;
slots_ret = NULL;
out:
mutex_unlock(&swap_slots_cache_mutex);
if (slots)
vfree(slots);
if (slots_ret)
vfree(slots_ret);
return 0;
}
static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
bool free_slots)
{
struct swap_slots_cache *cache;
swp_entry_t *slots = NULL;
cache = &per_cpu(swp_slots, cpu);
if ((type & SLOTS_CACHE) && cache->slots) {
mutex_lock(&cache->alloc_lock);
swapcache_free_entries(cache->slots + cache->cur, cache->nr);
cache->cur = 0;
cache->nr = 0;
if (free_slots && cache->slots) {
vfree(cache->slots);
cache->slots = NULL;
}
mutex_unlock(&cache->alloc_lock);
}
if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
spin_lock_irq(&cache->free_lock);
swapcache_free_entries(cache->slots_ret, cache->n_ret);
cache->n_ret = 0;
if (free_slots && cache->slots_ret) {
slots = cache->slots_ret;
cache->slots_ret = NULL;
}
spin_unlock_irq(&cache->free_lock);
if (slots)
vfree(slots);
}
}
static void __drain_swap_slots_cache(unsigned int type)
{
unsigned int cpu;
/*
* This function is called during
* 1) swapoff, when we have to make sure no
* left over slots are in cache when we remove
* a swap device;
* 2) disabling of swap slot cache, when we run low
* on swap slots when allocating memory and need
* to return swap slots to global pool.
*
* We cannot acquire cpu hot plug lock here as
* this function can be invoked in the cpu
* hot plug path:
* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
* -> memory allocation -> direct reclaim -> get_swap_page
* -> drain_swap_slots_cache
*
* Hence the loop over current online cpu below could miss cpu that
* is being brought online but not yet marked as online.
* That is okay as we do not schedule and run anything on a
* cpu before it has been marked online. Hence, we will not
* fill any swap slots in slots cache of such cpu.
* There are no slots on such cpu that need to be drained.
*/
for_each_online_cpu(cpu)
drain_slots_cache_cpu(cpu, type, false);
}
static int free_slot_cache(unsigned int cpu)
{
mutex_lock(&swap_slots_cache_mutex);
drain_slots_cache_cpu(cpu, SLOTS_CACHE | SLOTS_CACHE_RET, true);
mutex_unlock(&swap_slots_cache_mutex);
return 0;
}
int enable_swap_slots_cache(void)
{
int ret = 0;
mutex_lock(&swap_slots_cache_enable_mutex);
if (swap_slot_cache_initialized) {
__reenable_swap_slots_cache();
goto out_unlock;
}
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
alloc_swap_slot_cache, free_slot_cache);
if (ret < 0)
goto out_unlock;
swap_slot_cache_initialized = true;
__reenable_swap_slots_cache();
out_unlock:
mutex_unlock(&swap_slots_cache_enable_mutex);
return 0;
}
/* called with swap slot cache's alloc lock held */
static int refill_swap_slots_cache(struct swap_slots_cache *cache)
{
if (!use_swap_slot_cache || cache->nr)
return 0;
cache->cur = 0;
if (swap_slot_cache_active)
cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, cache->slots);
return cache->nr;
}
int free_swap_slot(swp_entry_t entry)
{
struct swap_slots_cache *cache;
cache = &get_cpu_var(swp_slots);
if (use_swap_slot_cache && cache->slots_ret) {
spin_lock_irq(&cache->free_lock);
/* Swap slots cache may be deactivated before acquiring lock */
if (!use_swap_slot_cache) {
spin_unlock_irq(&cache->free_lock);
goto direct_free;
}
if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
/*
* Return slots to global pool.
* The current swap_map value is SWAP_HAS_CACHE.
* Set it to 0 to indicate it is available for
* allocation in global pool
*/
swapcache_free_entries(cache->slots_ret, cache->n_ret);
cache->n_ret = 0;
}
cache->slots_ret[cache->n_ret++] = entry;
spin_unlock_irq(&cache->free_lock);
} else {
direct_free:
swapcache_free_entries(&entry, 1);
}
put_cpu_var(swp_slots);
return 0;
}
swp_entry_t get_swap_page(void)
{
swp_entry_t entry, *pentry;
struct swap_slots_cache *cache;
/*
* Preemption is allowed here, because we may sleep
* in refill_swap_slots_cache(). But it is safe, because
* accesses to the per-CPU data structure are protected by the
* mutex cache->alloc_lock.
*
* The alloc path here does not touch cache->slots_ret
* so cache->free_lock is not taken.
*/
cache = raw_cpu_ptr(&swp_slots);
entry.val = 0;
if (check_cache_active()) {
mutex_lock(&cache->alloc_lock);
if (cache->slots) {
repeat:
if (cache->nr) {
pentry = &cache->slots[cache->cur++];
entry = *pentry;
pentry->val = 0;
cache->nr--;
} else {
if (refill_swap_slots_cache(cache))
goto repeat;
}
}
mutex_unlock(&cache->alloc_lock);
if (entry.val)
return entry;
}
get_swap_pages(1, &entry);
return entry;
}
#endif /* CONFIG_SWAP */