From: Minchan Kim <[email protected]> Frontswap initialization routine depends on swap_lock, which want to be atomic about frontswap's first appearance. IOW, frontswap is not present and will fail all calls OR frontswap is fully functional but if new swap_info_struct isn't registered by enable_swap_info, swap subsystem doesn't start I/O so there is no race between init procedure and page I/O working on frontswap.
So let's remove unnecessary swap_lock dependency. Cc: Dan Magenheimer <[email protected]> Signed-off-by: Minchan Kim <[email protected]> [v1: Rebased on my branch, reworked to work with backends loading late] [v2: Added a check for !map] [v3: Made the invalidate path follow the init path] [v4: Address comments by Wanpeng Li <[email protected]>] Signed-off-by: Konrad Rzeszutek Wilk <[email protected]> --- include/linux/frontswap.h | 6 +++--- mm/frontswap.c | 29 ++++++++++++++++++++++------- mm/swapfile.c | 18 +++++++++--------- 3 files changed, 34 insertions(+), 19 deletions(-) diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h index 8d24167..c120b90 100644 --- a/include/linux/frontswap.h +++ b/include/linux/frontswap.h @@ -20,7 +20,7 @@ extern void frontswap_writethrough(bool); #define FRONTSWAP_HAS_EXCLUSIVE_GETS extern void frontswap_tmem_exclusive_gets(bool); -extern void __frontswap_init(unsigned type); +extern void __frontswap_init(unsigned type, unsigned long *map); extern int __frontswap_store(struct page *page); extern int __frontswap_load(struct page *page); extern void __frontswap_invalidate_page(unsigned, pgoff_t); @@ -122,9 +122,9 @@ static inline void frontswap_invalidate_area(unsigned type) __frontswap_invalidate_area(type); } -static inline void frontswap_init(unsigned type) +static inline void frontswap_init(unsigned type, unsigned long *map) { - __frontswap_init(type); + __frontswap_init(type, map); } #endif /* _LINUX_FRONTSWAP_H */ diff --git a/mm/frontswap.c b/mm/frontswap.c index ebf4c18..c84fc3b 100644 --- a/mm/frontswap.c +++ b/mm/frontswap.c @@ -127,8 +127,13 @@ struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops) int i; for (i = 0; i < MAX_SWAPFILES; i++) { - if (test_and_clear_bit(i, need_init)) + if (test_and_clear_bit(i, need_init)) { + struct swap_info_struct *sis = swap_info[i]; + /* __frontswap_init _should_ have set it! */ + if (!sis->frontswap_map) + return ERR_PTR(-EINVAL); ops->init(i); + } } /* * We MUST have frontswap_ops set _after_ the frontswap_init's @@ -166,16 +171,26 @@ EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); * * Can be called without any backend driver is registered. */ -void __frontswap_init(unsigned type) +void __frontswap_init(unsigned type, unsigned long *map) { struct swap_info_struct *sis = swap_info[type]; - if (static_key_false(&frontswap_key)) { - BUG_ON(sis == NULL); - if (sis->frontswap_map == NULL) - return; + BUG_ON(sis == NULL); + + /* + * p->frontswap is a bitmap that we MUST have to figure out which page + * has gone in frontswap. Without it there is no point of continuing. + */ + if (WARN_ON(!map)) + return; + /* + * Irregardless of whether the frontswap backend has been loaded + * before this function or it will be later, we _MUST_ have the + * p->frontswap set to something valid to work properly. + */ + frontswap_map_set(sis, map); + if (static_key_false(&frontswap_key)) frontswap_ops->init(type); - } else { BUG_ON(type > MAX_SWAPFILES); set_bit(type, need_init); diff --git a/mm/swapfile.c b/mm/swapfile.c index e97a0e5..086c287 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1444,8 +1444,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) } static void _enable_swap_info(struct swap_info_struct *p, int prio, - unsigned char *swap_map, - unsigned long *frontswap_map) + unsigned char *swap_map) { int i, prev; @@ -1454,11 +1453,9 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio, else p->prio = --least_priority; p->swap_map = swap_map; - frontswap_map_set(p, frontswap_map); p->flags |= SWP_WRITEOK; nr_swap_pages += p->pages; total_swap_pages += p->pages; - /* insert swap space into swap_list: */ prev = -1; for (i = swap_list.head; i >= 0; i = swap_info[i]->next) { @@ -1477,16 +1474,16 @@ static void enable_swap_info(struct swap_info_struct *p, int prio, unsigned char *swap_map, unsigned long *frontswap_map) { + frontswap_init(p->type, frontswap_map); spin_lock(&swap_lock); - _enable_swap_info(p, prio, swap_map, frontswap_map); - frontswap_init(p->type); + _enable_swap_info(p, prio, swap_map); spin_unlock(&swap_lock); } static void reinsert_swap_info(struct swap_info_struct *p) { spin_lock(&swap_lock); - _enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p)); + _enable_swap_info(p, p->prio, p->swap_map); spin_unlock(&swap_lock); } @@ -1494,6 +1491,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) { struct swap_info_struct *p = NULL; unsigned char *swap_map; + unsigned long *frontswap_map; struct file *swap_file, *victim; struct address_space *mapping; struct inode *inode; @@ -1588,11 +1586,13 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) swap_map = p->swap_map; p->swap_map = NULL; p->flags = 0; - frontswap_invalidate_area(type); + frontswap_map = frontswap_map_get(p); + frontswap_map_set(p, NULL); spin_unlock(&swap_lock); + frontswap_invalidate_area(type); mutex_unlock(&swapon_mutex); vfree(swap_map); - vfree(frontswap_map_get(p)); + vfree(frontswap_map); /* Destroy swap account informatin */ swap_cgroup_swapoff(type); -- 1.8.0.2 _______________________________________________ devel mailing list [email protected] http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
