LinuxLists.cc - [PATCH -next 0/3] Delay the initializaton of zswap

2022-08-25 14:04:56

Subject: [PATCH -next 0/3] Delay the initializaton of zswap

In the initialization of zswap, about 18MB memory will be allocated for
zswap_pool. Since not all users use zswap, the memory may be wasted. Save
the memory for these users by delaying the initialization of zswap to
first enablement.

Liu Shixin (3):
mm/zswap: replace zswap_init_{started/failed} with zswap_init_state
mm/zswap: delay the initializaton of zswap until the first enablement
mm/zswap: skip confusing print info

mm/zswap.c | 75 +++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 57 insertions(+), 18 deletions(-)

--
2.25.1

2022-08-25 14:05:29

by Liu Shixin

[permalink] [raw]

Subject: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

In the initialization of zswap, about 18MB memory will be allocated for
zswap_pool in my machine. Since not all users use zswap, the memory may be
wasted. Save the memory for these users by delaying the initialization of
zswap to first enablement.

Signed-off-by: Liu Shixin <[email protected]>
---
mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++---------
1 file changed, 39 insertions(+), 9 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 84e38300f571..90df72aceb08 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -81,6 +81,8 @@ static bool zswap_pool_reached_full;

#define ZSWAP_PARAM_UNSET ""

+static int zswap_setup(void);
+
/* Enable/disable zswap */
static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
static int zswap_enabled_param_set(const char *,
@@ -220,6 +222,8 @@ static atomic_t zswap_pools_count = ATOMIC_INIT(0);

/* init state */
static int zswap_init_state;
+/* used to ensure the integrity of initialization */
+static DEFINE_MUTEX(zswap_init_lock);

/* init completed, but couldn't create the initial pool */
static bool zswap_has_pool;
@@ -273,13 +277,13 @@ static void zswap_update_total_size(void)
**********************************/
static struct kmem_cache *zswap_entry_cache;

-static int __init zswap_entry_cache_create(void)
+static int zswap_entry_cache_create(void)
{
zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
return zswap_entry_cache == NULL;
}

-static void __init zswap_entry_cache_destroy(void)
+static void zswap_entry_cache_destroy(void)
{
kmem_cache_destroy(zswap_entry_cache);
}
@@ -664,7 +668,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
return NULL;
}

-static __init struct zswap_pool *__zswap_pool_create_fallback(void)
+static struct zswap_pool *__zswap_pool_create_fallback(void)
{
bool has_comp, has_zpool;

@@ -782,11 +786,17 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
return 0;

- /* if this is load-time (pre-init) param setting,
+ /*
+ * if zswap has not been initialized,
* don't create a pool; that's done during init.
*/
- if (zswap_init_state == ZSWAP_UNINIT)
- return param_set_charp(s, kp);
+ mutex_lock(&zswap_init_lock);
+ if (zswap_init_state == ZSWAP_UNINIT) {
+ ret = param_set_charp(s, kp);
+ mutex_unlock(&zswap_init_lock);
+ return ret;
+ }
+ mutex_unlock(&zswap_init_lock);

if (!type) {
if (!zpool_has_pool(s)) {
@@ -876,6 +886,14 @@ static int zswap_zpool_param_set(const char *val,
static int zswap_enabled_param_set(const char *val,
const struct kernel_param *kp)
{
+ if (system_state == SYSTEM_RUNNING) {
+ mutex_lock(&zswap_init_lock);
+ if (zswap_setup()) {
+ mutex_unlock(&zswap_init_lock);
+ return -ENODEV;
+ }
+ mutex_unlock(&zswap_init_lock);
+ }
if (zswap_init_state == ZSWAP_INIT_FAILED) {
pr_err("can't enable, initialization failed\n");
return -ENODEV;
@@ -1432,7 +1450,7 @@ static const struct frontswap_ops zswap_frontswap_ops = {

static struct dentry *zswap_debugfs_root;

-static int __init zswap_debugfs_init(void)
+static int zswap_debugfs_init(void)
{
if (!debugfs_initialized())
return -ENODEV;
@@ -1463,7 +1481,7 @@ static int __init zswap_debugfs_init(void)
return 0;
}
#else
-static int __init zswap_debugfs_init(void)
+static int zswap_debugfs_init(void)
{
return 0;
}
@@ -1472,11 +1490,14 @@ static int __init zswap_debugfs_init(void)
/*********************************
* module init and exit
**********************************/
-static int __init init_zswap(void)
+static int zswap_setup(void)
{
struct zswap_pool *pool;
int ret;

+ if (zswap_init_state != ZSWAP_UNINIT)
+ return 0;
+
if (zswap_entry_cache_create()) {
pr_err("entry cache creation failed\n");
goto cache_fail;
@@ -1534,6 +1555,15 @@ static int __init init_zswap(void)
zswap_enabled = false;
return -ENOMEM;
}
+
+static int __init init_zswap(void)
+{
+ /* skip init if zswap is disabled when system startup */
+ if (!zswap_enabled)
+ return 0;
+ return zswap_setup();
+}
+
/* must be late so crypto has time to come up */
late_initcall(init_zswap);

--
2.25.1

2022-08-25 14:21:10

by Liu Shixin

[permalink] [raw]

Subject: [PATCH -next 3/3] mm/zswap: skip confusing print info

It's confusing when we disable zswap while zswap is init failed or has no
pool. If no change required, just return directly.

Signed-off-by: Liu Shixin <[email protected]>
---
mm/zswap.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 90df72aceb08..fdf376f239fd 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -886,6 +886,15 @@ static int zswap_zpool_param_set(const char *val,
static int zswap_enabled_param_set(const char *val,
const struct kernel_param *kp)
{
+ bool res;
+
+ if (kstrtobool(val, &res))
+ return -EINVAL;
+
+ /* no change required */
+ if (res == *(bool *)kp->arg)
+ return 0;
+
if (system_state == SYSTEM_RUNNING) {
mutex_lock(&zswap_init_lock);
if (zswap_setup()) {
--
2.25.1

2022-08-25 14:22:43

by Liu Shixin

[permalink] [raw]

Subject: [PATCH -next 1/3] mm/zswap: replace zswap_init_{started/failed} with zswap_init_state

zswap_init_started indicates that the initialization is started. And
zswap_init_failed indicates that the initialization is failed. As we will
support to init zswap after system startup, it's necessary to add a state
to indicate the initialization is complete and succeed to avoid
concurrency issues. Since we don't care about the difference between
init started with init completion. We only need three states:
uninitialized, initial failed, initial succeed.

Signed-off-by: Liu Shixin <[email protected]>
---
mm/zswap.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 2d48fd59cc7a..84e38300f571 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -214,11 +214,12 @@ static DEFINE_SPINLOCK(zswap_pools_lock);
/* pool counter to provide unique names to zpool */
static atomic_t zswap_pools_count = ATOMIC_INIT(0);

-/* used by param callback function */
-static bool zswap_init_started;
+#define ZSWAP_UNINIT 0
+#define ZSWAP_INIT_SUCCEED 1
+#define ZSWAP_INIT_FAILED 2

-/* fatal error during init */
-static bool zswap_init_failed;
+/* init state */
+static int zswap_init_state;

/* init completed, but couldn't create the initial pool */
static bool zswap_has_pool;
@@ -772,7 +773,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
char *s = strstrip((char *)val);
int ret;

- if (zswap_init_failed) {
+ if (zswap_init_state == ZSWAP_INIT_FAILED) {
pr_err("can't set param, initialization failed\n");
return -ENODEV;
}
@@ -784,7 +785,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
/* if this is load-time (pre-init) param setting,
* don't create a pool; that's done during init.
*/
- if (!zswap_init_started)
+ if (zswap_init_state == ZSWAP_UNINIT)
return param_set_charp(s, kp);

if (!type) {
@@ -875,11 +876,11 @@ static int zswap_zpool_param_set(const char *val,
static int zswap_enabled_param_set(const char *val,
const struct kernel_param *kp)
{
- if (zswap_init_failed) {
+ if (zswap_init_state == ZSWAP_INIT_FAILED) {
pr_err("can't enable, initialization failed\n");
return -ENODEV;
}
- if (!zswap_has_pool && zswap_init_started) {
+ if (!zswap_has_pool && zswap_init_state == ZSWAP_INIT_SUCCEED) {
pr_err("can't enable, no pool configured\n");
return -ENODEV;
}
@@ -1476,8 +1477,6 @@ static int __init init_zswap(void)
struct zswap_pool *pool;
int ret;

- zswap_init_started = true;
-
if (zswap_entry_cache_create()) {
pr_err("entry cache creation failed\n");
goto cache_fail;
@@ -1517,6 +1516,7 @@ static int __init init_zswap(void)
goto destroy_wq;
if (zswap_debugfs_init())
pr_warn("debugfs initialization failed\n");
+ zswap_init_state = ZSWAP_INIT_SUCCEED;
return 0;

destroy_wq:
@@ -1530,7 +1530,7 @@ static int __init init_zswap(void)
zswap_entry_cache_destroy();
cache_fail:
/* if built-in, we aren't unloaded on failure; don't allow use */
- zswap_init_failed = true;
+ zswap_init_state = ZSWAP_INIT_FAILED;
zswap_enabled = false;
return -ENOMEM;
}
--
2.25.1

2022-08-26 02:19:08

by Andrew Morton

[permalink] [raw]

Subject: Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

On Thu, 25 Aug 2022 22:20:36 +0800 Liu Shixin <[email protected]> wrote:

> In the initialization of zswap, about 18MB memory will be allocated for
> zswap_pool in my machine. Since not all users use zswap, the memory may be
> wasted. Save the memory for these users by delaying the initialization of
> zswap to first enablement.
>
> ...
>
> +static int __init init_zswap(void)
> +{
> + /* skip init if zswap is disabled when system startup */
> + if (!zswap_enabled)
> + return 0;
> + return zswap_setup();
> +}
> +

I can't resist.

--- a/mm/zswap.c~mm-zswap-delay-the-initializaton-of-zswap-until-the-first-enablement-fix
+++ a/mm/zswap.c
@@ -1556,7 +1556,7 @@ cache_fail:
return -ENOMEM;
}

-static int __init init_zswap(void)
+static int __init zswap_init(void)
{
/* skip init if zswap is disabled when system startup */
if (!zswap_enabled)
@@ -1565,7 +1565,7 @@ static int __init init_zswap(void)
}

/* must be late so crypto has time to come up */
-late_initcall(init_zswap);
+late_initcall(zswap_init);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Seth Jennings <[email protected]>");

It's the usual way and makes things more consistent.

2022-08-26 21:13:28

by Nathan Chancellor

[permalink] [raw]

Subject: Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

Hi Liu,

On Thu, Aug 25, 2022 at 10:20:36PM +0800, Liu Shixin wrote:
> In the initialization of zswap, about 18MB memory will be allocated for
> zswap_pool in my machine. Since not all users use zswap, the memory may be
> wasted. Save the memory for these users by delaying the initialization of
> zswap to first enablement.
>
> Signed-off-by: Liu Shixin <[email protected]>
> ---
> mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 39 insertions(+), 9 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 84e38300f571..90df72aceb08 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -81,6 +81,8 @@ static bool zswap_pool_reached_full;
>
> #define ZSWAP_PARAM_UNSET ""
>
> +static int zswap_setup(void);
> +
> /* Enable/disable zswap */
> static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
> static int zswap_enabled_param_set(const char *,
> @@ -220,6 +222,8 @@ static atomic_t zswap_pools_count = ATOMIC_INIT(0);
>
> /* init state */
> static int zswap_init_state;
> +/* used to ensure the integrity of initialization */
> +static DEFINE_MUTEX(zswap_init_lock);
>
> /* init completed, but couldn't create the initial pool */
> static bool zswap_has_pool;
> @@ -273,13 +277,13 @@ static void zswap_update_total_size(void)
> **********************************/
> static struct kmem_cache *zswap_entry_cache;
>
> -static int __init zswap_entry_cache_create(void)
> +static int zswap_entry_cache_create(void)
> {
> zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
> return zswap_entry_cache == NULL;
> }
>
> -static void __init zswap_entry_cache_destroy(void)
> +static void zswap_entry_cache_destroy(void)
> {
> kmem_cache_destroy(zswap_entry_cache);
> }
> @@ -664,7 +668,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> return NULL;
> }
>
> -static __init struct zswap_pool *__zswap_pool_create_fallback(void)
> +static struct zswap_pool *__zswap_pool_create_fallback(void)
> {
> bool has_comp, has_zpool;
>
> @@ -782,11 +786,17 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
> if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
> return 0;
>
> - /* if this is load-time (pre-init) param setting,
> + /*
> + * if zswap has not been initialized,
> * don't create a pool; that's done during init.
> */
> - if (zswap_init_state == ZSWAP_UNINIT)
> - return param_set_charp(s, kp);
> + mutex_lock(&zswap_init_lock);
> + if (zswap_init_state == ZSWAP_UNINIT) {
> + ret = param_set_charp(s, kp);
> + mutex_unlock(&zswap_init_lock);
> + return ret;
> + }
> + mutex_unlock(&zswap_init_lock);
>
> if (!type) {
> if (!zpool_has_pool(s)) {
> @@ -876,6 +886,14 @@ static int zswap_zpool_param_set(const char *val,
> static int zswap_enabled_param_set(const char *val,
> const struct kernel_param *kp)
> {
> + if (system_state == SYSTEM_RUNNING) {
> + mutex_lock(&zswap_init_lock);
> + if (zswap_setup()) {
> + mutex_unlock(&zswap_init_lock);
> + return -ENODEV;
> + }
> + mutex_unlock(&zswap_init_lock);
> + }
> if (zswap_init_state == ZSWAP_INIT_FAILED) {
> pr_err("can't enable, initialization failed\n");
> return -ENODEV;
> @@ -1432,7 +1450,7 @@ static const struct frontswap_ops zswap_frontswap_ops = {
>
> static struct dentry *zswap_debugfs_root;
>
> -static int __init zswap_debugfs_init(void)
> +static int zswap_debugfs_init(void)
> {
> if (!debugfs_initialized())
> return -ENODEV;
> @@ -1463,7 +1481,7 @@ static int __init zswap_debugfs_init(void)
> return 0;
> }
> #else
> -static int __init zswap_debugfs_init(void)
> +static int zswap_debugfs_init(void)
> {
> return 0;
> }
> @@ -1472,11 +1490,14 @@ static int __init zswap_debugfs_init(void)
> /*********************************
> * module init and exit
> **********************************/
> -static int __init init_zswap(void)
> +static int zswap_setup(void)
> {
> struct zswap_pool *pool;
> int ret;
>
> + if (zswap_init_state != ZSWAP_UNINIT)
> + return 0;
> +
> if (zswap_entry_cache_create()) {
> pr_err("entry cache creation failed\n");
> goto cache_fail;
> @@ -1534,6 +1555,15 @@ static int __init init_zswap(void)
> zswap_enabled = false;
> return -ENOMEM;
> }
> +
> +static int __init init_zswap(void)
> +{
> + /* skip init if zswap is disabled when system startup */
> + if (!zswap_enabled)
> + return 0;
> + return zswap_setup();
> +}
> +
> /* must be late so crypto has time to come up */
> late_initcall(init_zswap);
>
> --
> 2.25.1
>
>

This change is in -next as commit 22100432cf14 ("mm/zswap: delay the
initializaton of zswap until the first enablement"). I just bisected my
arm64 test system running Fedora failing to boot due to that commit,
with the 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 ]---

This is with Fedora's configuration:

https://src.fedoraproject.org/rpms/kernel/raw/rawhide/f/kernel-aarch64-fedora.config

If there is any more information I can provide or patches I can test, I
am more than happy to do so!

Cheers,
Nathan

2022-08-27 02:10:13

by Kefeng Wang

[permalink] [raw]

Subject: Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

2022-08-27 02:44:15

by Andrew Morton

[permalink] [raw]

Subject: Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

On Fri, 26 Aug 2022 13:25:41 -0700 Nathan Chancellor <[email protected]> wrote:

> Hi Liu,
>
> On Thu, Aug 25, 2022 at 10:20:36PM +0800, Liu Shixin wrote:
> > In the initialization of zswap, about 18MB memory will be allocated for
> > zswap_pool in my machine. Since not all users use zswap, the memory may be
> > wasted. Save the memory for these users by delaying the initialization of
> > zswap to first enablement.
> >
>
> ...
>
> This change is in -next as commit 22100432cf14 ("mm/zswap: delay the
> initializaton of zswap until the first enablement"). I just bisected my
> arm64 test system running Fedora failing to boot due to that commit,
> with the following stack trace:
>

Thanks. Sorry. I dropped the series.

2022-08-27 11:04:55

by Liu Shixin

[permalink] [raw]

Subject: Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

On 2022/8/27 4:25, Nathan Chancellor wrote:
> Hi Liu,
>
> On Thu, Aug 25, 2022 at 10:20:36PM +0800, Liu Shixin wrote:
>> In the initialization of zswap, about 18MB memory will be allocated for
>> zswap_pool in my machine. Since not all users use zswap, the memory may be
>> wasted. Save the memory for these users by delaying the initialization of
>> zswap to first enablement.
>>
>> Signed-off-by: Liu Shixin <[email protected]>
>> ---
>> mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++---------
>> 1 file changed, 39 insertions(+), 9 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 84e38300f571..90df72aceb08 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -81,6 +81,8 @@ static bool zswap_pool_reached_full;
>>
>> #define ZSWAP_PARAM_UNSET ""
>>
>> +static int zswap_setup(void);
>> +
>> /* Enable/disable zswap */
>> static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
>> static int zswap_enabled_param_set(const char *,
>> @@ -220,6 +222,8 @@ static atomic_t zswap_pools_count = ATOMIC_INIT(0);
>>
>> /* init state */
>> static int zswap_init_state;
>> +/* used to ensure the integrity of initialization */
>> +static DEFINE_MUTEX(zswap_init_lock);
>>
>> /* init completed, but couldn't create the initial pool */
>> static bool zswap_has_pool;
>> @@ -273,13 +277,13 @@ static void zswap_update_total_size(void)
>> **********************************/
>> static struct kmem_cache *zswap_entry_cache;
>>
>> -static int __init zswap_entry_cache_create(void)
>> +static int zswap_entry_cache_create(void)
>> {
>> zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
>> return zswap_entry_cache == NULL;
>> }
>>
>> -static void __init zswap_entry_cache_destroy(void)
>> +static void zswap_entry_cache_destroy(void)
>> {
>> kmem_cache_destroy(zswap_entry_cache);
>> }
>> @@ -664,7 +668,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
>> return NULL;
>> }
>>
>> -static __init struct zswap_pool *__zswap_pool_create_fallback(void)
>> +static struct zswap_pool *__zswap_pool_create_fallback(void)
>> {
>> bool has_comp, has_zpool;
>>
>> @@ -782,11 +786,17 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
>> if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
>> return 0;
>>
>> - /* if this is load-time (pre-init) param setting,
>> + /*
>> + * if zswap has not been initialized,
>> * don't create a pool; that's done during init.
>> */
>> - if (zswap_init_state == ZSWAP_UNINIT)
>> - return param_set_charp(s, kp);
>> + mutex_lock(&zswap_init_lock);
>> + if (zswap_init_state == ZSWAP_UNINIT) {
>> + ret = param_set_charp(s, kp);
>> + mutex_unlock(&zswap_init_lock);
>> + return ret;
>> + }
>> + mutex_unlock(&zswap_init_lock);
>>
>> if (!type) {
>> if (!zpool_has_pool(s)) {
>> @@ -876,6 +886,14 @@ static int zswap_zpool_param_set(const char *val,
>> static int zswap_enabled_param_set(const char *val,
>> const struct kernel_param *kp)
>> {
>> + if (system_state == SYSTEM_RUNNING) {
>> + mutex_lock(&zswap_init_lock);
>> + if (zswap_setup()) {
>> + mutex_unlock(&zswap_init_lock);
>> + return -ENODEV;
>> + }
>> + mutex_unlock(&zswap_init_lock);
>> + }
>> if (zswap_init_state == ZSWAP_INIT_FAILED) {
>> pr_err("can't enable, initialization failed\n");
>> return -ENODEV;
>> @@ -1432,7 +1450,7 @@ static const struct frontswap_ops zswap_frontswap_ops = {
>>
>> static struct dentry *zswap_debugfs_root;
>>
>> -static int __init zswap_debugfs_init(void)
>> +static int zswap_debugfs_init(void)
>> {
>> if (!debugfs_initialized())
>> return -ENODEV;
>> @@ -1463,7 +1481,7 @@ static int __init zswap_debugfs_init(void)
>> return 0;
>> }
>> #else
>> -static int __init zswap_debugfs_init(void)
>> +static int zswap_debugfs_init(void)
>> {
>> return 0;
>> }
>> @@ -1472,11 +1490,14 @@ static int __init zswap_debugfs_init(void)
>> /*********************************
>> * module init and exit
>> **********************************/
>> -static int __init init_zswap(void)
>> +static int zswap_setup(void)
>> {
>> struct zswap_pool *pool;
>> int ret;
>>
>> + if (zswap_init_state != ZSWAP_UNINIT)
>> + return 0;
>> +
>> if (zswap_entry_cache_create()) {
>> pr_err("entry cache creation failed\n");
>> goto cache_fail;
>> @@ -1534,6 +1555,15 @@ static int __init init_zswap(void)
>> zswap_enabled = false;
>> return -ENOMEM;
>> }
>> +
>> +static int __init init_zswap(void)
>> +{
>> + /* skip init if zswap is disabled when system startup */
>> + if (!zswap_enabled)
>> + return 0;
>> + return zswap_setup();
>> +}
>> +
>> /* must be late so crypto has time to come up */
>> late_initcall(init_zswap);
>>
>> --
>> 2.25.1
>>
>>
> This change is in -next as commit 22100432cf14 ("mm/zswap: delay the
> initializaton of zswap until the first enablement"). I just bisected my
> arm64 test system running Fedora failing to boot due to that commit,
> with the 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 ]---
>
> This is with Fedora's configuration:
>
> https://src.fedoraproject.org/rpms/kernel/raw/rawhide/f/kernel-aarch64-fedora.config
>
> If there is any more information I can provide or patches I can test, I
> am more than happy to do so!
>
> Cheers,
> Nathan
> .
Thanks for your reporting, it looks likt that this problem will occur when zswap is not initial succeed.
zswap is the only backend for frontswap for now, but frontswap does not check if zswap is valid.

I fix this problem in v3 by skipping frontswap_ops->init in frontswap_init if zswap is not ready.

Link: https://lore.kernel.org/all/[email protected]/

Thanks,