Hi Minchan and Konrad,
On Fri, Feb 01, 2013 at 03:23:02PM -0500, Konrad Rzeszutek Wilk wrote:
>From: Minchan Kim <minchan@xxxxxxxxxx>
>
>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 unncessary swap_lock dependency.
>
>Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
>Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
>[v1: Rebased on my branch, reworked to work with backends loading late]
>[v2: Added a check for !map]
>Signed-off-by: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
>
>squash
>---
> include/linux/frontswap.h | 6 +++---
> mm/frontswap.c | 12 +++++++++---
> mm/swapfile.c | 7 ++++++-
> 3 files changed, 18 insertions(+), 7 deletions(-)
>
>diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
>index 612c176..3d72f14 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..8254a6a 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];
>+ /* enable_swap_info _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
>@@ -166,14 +171,15 @@ 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)
>+ if (!map)
> return;
>+ frontswap_map_set(sis, map);
> frontswap_ops->init(type);
> }
> else {
>diff --git a/mm/swapfile.c b/mm/swapfile.c
>index e97a0e5..c1c3a62 100644
>--- a/mm/swapfile.c
>+++ b/mm/swapfile.c
>@@ -1454,6 +1454,10 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio,
> else
> p->prio = --least_priority;
> p->swap_map = swap_map;
>+ /*
>+ * This is required for frontswap to handle backends loading
>+ * after the swap has been activated.
>+ */
> frontswap_map_set(p, frontswap_map);
Why set frontswap_map twice?
> p->flags |= SWP_WRITEOK;
> nr_swap_pages += p->pages;
>@@ -1477,9 +1481,9 @@ 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);
> spin_unlock(&swap_lock);
> }
>
>@@ -1589,6 +1593,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
> p->swap_map = NULL;
> p->flags = 0;
> frontswap_invalidate_area(type);
>+ frontswap_map_set(p, NULL);
This will lead to memory leak, the memory will not be freed since
vfree(frontswap_map_get(p)); will miss it. :(
> spin_unlock(&swap_lock);
> mutex_unlock(&swapon_mutex);
> vfree(swap_map);
>--
>1.7.11.7
>
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