diff options
| -rw-r--r-- | include/linux/swap.h | 5 | ||||
| -rw-r--r-- | mm/swapfile.c | 79 |
2 files changed, 52 insertions, 32 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h index 144727041e78..c9e7fea10b83 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -177,7 +177,6 @@ enum { SWP_PAGE_DISCARD = (1 << 10), /* freed swap page-cluster discards */ SWP_STABLE_WRITES = (1 << 11), /* no overwrite PG_writeback pages */ SWP_SYNCHRONOUS_IO = (1 << 12), /* synchronous IO is efficient */ - SWP_VALID = (1 << 13), /* swap is valid to be operated on? */ /* add others here before... */ SWP_SCANNING = (1 << 14), /* refcount in scan_swap_map */ }; @@ -240,6 +239,7 @@ struct swap_cluster_list { * The in-memory structure used to track swap areas. */ struct swap_info_struct { + struct percpu_ref users; /* indicate and keep swap device valid. */ unsigned long flags; /* SWP_USED etc: see above */ signed short prio; /* swap priority of this type */ struct plist_node list; /* entry in swap_active_head */ @@ -260,6 +260,7 @@ struct swap_info_struct { struct block_device *bdev; /* swap device or bdev of swap file */ struct file *swap_file; /* seldom referenced */ unsigned int old_block_size; /* seldom referenced */ + struct completion comp; /* seldom referenced */ #ifdef CONFIG_FRONTSWAP unsigned long *frontswap_map; /* frontswap in-use, one bit per page */ atomic_t frontswap_pages; /* frontswap pages in-use counter */ @@ -511,7 +512,7 @@ sector_t swap_page_sector(struct page *page); static inline void put_swap_device(struct swap_info_struct *si) { - rcu_read_unlock(); + percpu_ref_put(&si->users); } #else /* CONFIG_SWAP */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 996afa8131c8..a9a04a5360d9 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -39,6 +39,7 @@ #include <linux/export.h> #include <linux/swap_slots.h> #include <linux/sort.h> +#include <linux/completion.h> #include <asm/tlbflush.h> #include <linux/swapops.h> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work) spin_unlock(&si->lock); } +static void swap_users_ref_free(struct percpu_ref *ref) +{ + struct swap_info_struct *si; + + si = container_of(ref, struct swap_info_struct, users); + complete(&si->comp); +} + static void alloc_cluster(struct swap_info_struct *si, unsigned long idx) { struct swap_cluster_info *ci = si->cluster_info; @@ -1270,18 +1279,12 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p, * via preventing the swap device from being swapoff, until * put_swap_device() is called. Otherwise return NULL. * - * The entirety of the RCU read critical section must come before the - * return from or after the call to synchronize_rcu() in - * enable_swap_info() or swapoff(). So if "si->flags & SWP_VALID" is - * true, the si->map, si->cluster_info, etc. must be valid in the - * critical section. - * * Notice that swapoff or swapoff+swapon can still happen before the - * rcu_read_lock() in get_swap_device() or after the rcu_read_unlock() - * in put_swap_device() if there isn't any other way to prevent - * swapoff, such as page lock, page table lock, etc. The caller must - * be prepared for that. For example, the following situation is - * possible. + * percpu_ref_tryget_live() in get_swap_device() or after the + * percpu_ref_put() in put_swap_device() if there isn't any other way + * to prevent swapoff, such as page lock, page table lock, etc. The + * caller must be prepared for that. For example, the following + * situation is possible. * * CPU1 CPU2 * do_swap_page() @@ -1309,21 +1312,27 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry) si = swp_swap_info(entry); if (!si) goto bad_nofile; - - rcu_read_lock(); - if (data_race(!(si->flags & SWP_VALID))) - goto unlock_out; + if (!percpu_ref_tryget_live(&si->users)) + goto out; + /* + * Guarantee the si->users are checked before accessing other + * fields of swap_info_struct. + * + * Paired with the spin_unlock() after setup_swap_info() in + * enable_swap_info(). + */ + smp_rmb(); offset = swp_offset(entry); if (offset >= si->max) - goto unlock_out; + goto put_out; return si; bad_nofile: pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val); out: return NULL; -unlock_out: - rcu_read_unlock(); +put_out: + percpu_ref_put(&si->users); return NULL; } @@ -2466,7 +2475,7 @@ static void setup_swap_info(struct swap_info_struct *p, int prio, static void _enable_swap_info(struct swap_info_struct *p) { - p->flags |= SWP_WRITEOK | SWP_VALID; + p->flags |= SWP_WRITEOK; atomic_long_add(p->pages, &nr_swap_pages); total_swap_pages += p->pages; @@ -2497,10 +2506,9 @@ static void enable_swap_info(struct swap_info_struct *p, int prio, spin_unlock(&p->lock); spin_unlock(&swap_lock); /* - * Guarantee swap_map, cluster_info, etc. fields are valid - * between get/put_swap_device() if SWP_VALID bit is set + * Finished initializing swap device, now it's safe to reference it. */ - synchronize_rcu(); + percpu_ref_resurrect(&p->users); spin_lock(&swap_lock); spin_lock(&p->lock); _enable_swap_info(p); @@ -2616,16 +2624,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) reenable_swap_slots_cache_unlock(); - spin_lock(&swap_lock); - spin_lock(&p->lock); - p->flags &= ~SWP_VALID; /* mark swap device as invalid */ - spin_unlock(&p->lock); - spin_unlock(&swap_lock); /* - * wait for swap operations protected by get/put_swap_device() - * to complete + * Wait for swap operations protected by get/put_swap_device() + * to complete. + * + * We need synchronize_rcu() here to protect the accessing to + * the swap cache data structure. */ + percpu_ref_kill(&p->users); synchronize_rcu(); + wait_for_completion(&p->comp); flush_work(&p->discard_work); @@ -2857,6 +2865,12 @@ static struct swap_info_struct *alloc_swap_info(void) if (!p) return ERR_PTR(-ENOMEM); + if (percpu_ref_init(&p->users, swap_users_ref_free, + PERCPU_REF_INIT_DEAD, GFP_KERNEL)) { + kvfree(p); + return ERR_PTR(-ENOMEM); + } + spin_lock(&swap_lock); for (type = 0; type < nr_swapfiles; type++) { if (!(swap_info[type]->flags & SWP_USED)) @@ -2864,6 +2878,7 @@ static struct swap_info_struct *alloc_swap_info(void) } if (type >= MAX_SWAPFILES) { spin_unlock(&swap_lock); + percpu_ref_exit(&p->users); kvfree(p); return ERR_PTR(-EPERM); } @@ -2891,9 +2906,13 @@ static struct swap_info_struct *alloc_swap_info(void) plist_node_init(&p->avail_lists[i], 0); p->flags = SWP_USED; spin_unlock(&swap_lock); - kvfree(defer); + if (defer) { + percpu_ref_exit(&defer->users); + kvfree(defer); + } spin_lock_init(&p->lock); spin_lock_init(&p->cont_lock); + init_completion(&p->comp); return p; } |