[PATCH -next v4 1/6] Revert "frontswap: remove support for multiple ops"
From: Liu Shixin
Date: Mon Aug 29 2022 - 08:58:18 EST
This reverts commit 1da0d94a3ec8c5f3793b7be8538b55e60ebeefe3.
If zswap initial failed or has not been initial, frontswap_ops will be
NULL. In such situation, swap device would enable failed with following
stack trace:
Unable to handle kernel access to user memory outside uaccess routines at virtual address 0000000000000000
Mem abort info:
ESR = 0x0000000096000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
Data abort info:
ISV = 0, ISS = 0x00000004
CM = 0, WnR = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=00000020a4fab000
[0000000000000000] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 96000004 [#1] SMP
Modules linked in: zram fsl_dpaa2_eth pcs_lynx phylink ahci_qoriq crct10dif_ce ghash_ce sbsa_gwdt fsl_mc_dpio nvme lm90 nvme_core at803x xhci_plat_hcd rtc_fsl_ftm_alarm xgmac_mdio ahci_platform i2c_imx ip6_tables ip_tables fuse
Unloaded tainted modules: cppc_cpufreq():1
CPU: 10 PID: 761 Comm: swapon Not tainted 6.0.0-rc2-00454-g22100432cf14 #1
Hardware name: SolidRun Ltd. SolidRun CEX7 Platform, BIOS EDK II Jun 21 2022
pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : frontswap_init+0x38/0x60
lr : __do_sys_swapon+0x8a8/0x9f4
sp : ffff80000969bcf0
x29: ffff80000969bcf0 x28: ffff37bee0d8fc00 x27: ffff80000a7f5000
x26: fffffcdefb971e80 x25: ffffaba797453b90 x24: 0000000000000064
x23: ffff37c1f209d1a8 x22: ffff37bee880e000 x21: ffffaba797748560
x20: ffff37bee0d8fce4 x19: ffffaba797748488 x18: 0000000000000014
x17: 0000000030ec029a x16: ffffaba795a479b0 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000030 x12: 0000000000000001
x11: ffff37c63c0aba18 x10: 0000000000000000 x9 : ffffaba7956b8c88
x8 : ffff80000969bcd0 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000000 x3 : ffffaba79730f000
x2 : ffff37bee0d8fc00 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
frontswap_init+0x38/0x60
__do_sys_swapon+0x8a8/0x9f4
__arm64_sys_swapon+0x28/0x3c
invoke_syscall+0x78/0x100
el0_svc_common.constprop.0+0xd4/0xf4
do_el0_svc+0x38/0x4c
el0_svc+0x34/0x10c
el0t_64_sync_handler+0x11c/0x150
el0t_64_sync+0x190/0x194
Code: d000e283 910003fd f9006c41 f946d461 (f9400021)
---[ end trace 0000000000000000 ]---
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
include/linux/frontswap.h | 3 ++-
mm/frontswap.c | 50 +++++++++++++++++++++++++++++----------
mm/zswap.c | 8 ++-----
3 files changed, 42 insertions(+), 19 deletions(-)
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index a631bac12220..c5b2848d2240 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -13,9 +13,10 @@ struct frontswap_ops {
int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
+ struct frontswap_ops *next; /* private pointer to next ops */
};
-int frontswap_register_ops(const struct frontswap_ops *ops);
+extern void frontswap_register_ops(struct frontswap_ops *ops);
extern void frontswap_init(unsigned type, unsigned long *map);
extern int __frontswap_store(struct page *page);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 1a97610308cb..8d644f56a1d2 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -27,7 +27,10 @@ DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
* may be registered, but implementations can never deregister. This
* is a simple singly-linked list of all registered implementations.
*/
-static const struct frontswap_ops *frontswap_ops __read_mostly;
+static struct frontswap_ops *frontswap_ops __read_mostly;
+
+#define for_each_frontswap_ops(ops) \
+ for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
#ifdef CONFIG_DEBUG_FS
/*
@@ -94,14 +97,18 @@ static inline void inc_frontswap_invalidates(void) { }
/*
* Register operations for frontswap
*/
-int frontswap_register_ops(const struct frontswap_ops *ops)
+void frontswap_register_ops(struct frontswap_ops *ops)
{
- if (frontswap_ops)
- return -EINVAL;
+ /*
+ * Setting frontswap_ops must happen after the ops->init() calls
+ * above; cmpxchg implies smp_mb() which will ensure the init is
+ * complete at this point.
+ */
+ do {
+ ops->next = frontswap_ops;
+ } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
- frontswap_ops = ops;
static_branch_inc(&frontswap_enabled_key);
- return 0;
}
/*
@@ -110,6 +117,7 @@ int frontswap_register_ops(const struct frontswap_ops *ops)
void frontswap_init(unsigned type, unsigned long *map)
{
struct swap_info_struct *sis = swap_info[type];
+ struct frontswap_ops *ops;
VM_BUG_ON(sis == NULL);
@@ -125,7 +133,9 @@ void frontswap_init(unsigned type, unsigned long *map)
* p->frontswap set to something valid to work properly.
*/
frontswap_map_set(sis, map);
- frontswap_ops->init(type);
+
+ for_each_frontswap_ops(ops)
+ ops->init(type);
}
static bool __frontswap_test(struct swap_info_struct *sis,
@@ -164,6 +174,7 @@ int __frontswap_store(struct page *page)
int type = swp_type(entry);
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
+ struct frontswap_ops *ops;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(!PageLocked(page));
@@ -177,10 +188,16 @@ int __frontswap_store(struct page *page)
*/
if (__frontswap_test(sis, offset)) {
__frontswap_clear(sis, offset);
- frontswap_ops->invalidate_page(type, offset);
+ for_each_frontswap_ops(ops)
+ ops->invalidate_page(type, offset);
}
- ret = frontswap_ops->store(type, offset, page);
+ /* Try to store in each implementation, until one succeeds. */
+ for_each_frontswap_ops(ops) {
+ ret = ops->store(type, offset, page);
+ if (!ret) /* successful store */
+ break;
+ }
if (ret == 0) {
__frontswap_set(sis, offset);
inc_frontswap_succ_stores();
@@ -203,6 +220,7 @@ int __frontswap_load(struct page *page)
int type = swp_type(entry);
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
+ struct frontswap_ops *ops;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(!PageLocked(page));
@@ -212,7 +230,11 @@ int __frontswap_load(struct page *page)
return -1;
/* Try loading from each implementation, until one succeeds. */
- ret = frontswap_ops->load(type, offset, page);
+ for_each_frontswap_ops(ops) {
+ ret = ops->load(type, offset, page);
+ if (!ret) /* successful load */
+ break;
+ }
if (ret == 0)
inc_frontswap_loads();
return ret;
@@ -225,6 +247,7 @@ int __frontswap_load(struct page *page)
void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
struct swap_info_struct *sis = swap_info[type];
+ struct frontswap_ops *ops;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(sis == NULL);
@@ -232,7 +255,8 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
if (!__frontswap_test(sis, offset))
return;
- frontswap_ops->invalidate_page(type, offset);
+ for_each_frontswap_ops(ops)
+ ops->invalidate_page(type, offset);
__frontswap_clear(sis, offset);
inc_frontswap_invalidates();
}
@@ -244,6 +268,7 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
void __frontswap_invalidate_area(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
+ struct frontswap_ops *ops;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(sis == NULL);
@@ -251,7 +276,8 @@ void __frontswap_invalidate_area(unsigned type)
if (sis->frontswap_map == NULL)
return;
- frontswap_ops->invalidate_area(type);
+ for_each_frontswap_ops(ops)
+ ops->invalidate_area(type);
atomic_set(&sis->frontswap_pages, 0);
bitmap_zero(sis->frontswap_map, sis->max);
}
diff --git a/mm/zswap.c b/mm/zswap.c
index 2d48fd59cc7a..c22208df292a 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1415,7 +1415,7 @@ static void zswap_frontswap_init(unsigned type)
zswap_trees[type] = tree;
}
-static const struct frontswap_ops zswap_frontswap_ops = {
+static struct frontswap_ops zswap_frontswap_ops = {
.store = zswap_frontswap_store,
.load = zswap_frontswap_load,
.invalidate_page = zswap_frontswap_invalidate_page,
@@ -1512,15 +1512,11 @@ static int __init init_zswap(void)
if (!shrink_wq)
goto fallback_fail;
- ret = frontswap_register_ops(&zswap_frontswap_ops);
- if (ret)
- goto destroy_wq;
+ frontswap_register_ops(&zswap_frontswap_ops);
if (zswap_debugfs_init())
pr_warn("debugfs initialization failed\n");
return 0;
-destroy_wq:
- destroy_workqueue(shrink_wq);
fallback_fail:
if (pool)
zswap_pool_destroy(pool);
--
2.25.1