| Message ID | 20210420133048.6773-2-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | close various race windows for swap | expand |
Miaohe Lin <linmiaohe@huawei.com> writes: > Using current get/put_swap_device() to guard against concurrent swapoff > for some swap ops, e.g. swap_readpage(), looks terrible because they > might take really long time. This patch adds the percpu_ref support to > serialize against concurrent swapoff. Also we remove the SWP_VALID flag > because it's used together with RCU solution. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > include/linux/swap.h | 5 +-- > 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 149e77454e3c..a640fc84be5b 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 initialized swap device, now it's safe to reference it. s/initialized/initializing/ Otherwise looks good to me! Thanks! Reviewed-by: "Huang, Ying" <ying.huang@intel.com> > */ > - 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; > }
On 2021/4/21 9:05, Huang, Ying wrote: > Miaohe Lin <linmiaohe@huawei.com> writes: > >> Using current get/put_swap_device() to guard against concurrent swapoff >> for some swap ops, e.g. swap_readpage(), looks terrible because they >> might take really long time. This patch adds the percpu_ref support to >> serialize against concurrent swapoff. Also we remove the SWP_VALID flag >> because it's used together with RCU solution. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> include/linux/swap.h | 5 +-- >> 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 149e77454e3c..a640fc84be5b 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 initialized swap device, now it's safe to reference it. > > s/initialized/initializing/ > > Otherwise looks good to me! Thanks! > > Reviewed-by: "Huang, Ying" <ying.huang@intel.com> > Many thanks for your quick review and respond again. All these comments look good. Will fix it in V4. Thank you very much ! >> */ >> - 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; >> } > . >
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 149e77454e3c..a640fc84be5b 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 initialized 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; }
Using current get/put_swap_device() to guard against concurrent swapoff for some swap ops, e.g. swap_readpage(), looks terrible because they might take really long time. This patch adds the percpu_ref support to serialize against concurrent swapoff. Also we remove the SWP_VALID flag because it's used together with RCU solution. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- include/linux/swap.h | 5 +-- mm/swapfile.c | 79 +++++++++++++++++++++++++++----------------- 2 files changed, 52 insertions(+), 32 deletions(-)