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hwrng: core - Stop/start hwrng_fillfn() kthread before/after suspend-resume

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The hwrng_fillfn() kernel thread accesses the RNG device directly. During
suspend and resume sequences, hwrng_fillfn() may attempt to access the RNG
device while it is suspended. To address this, the hwrng_fillfn() kernel
thread is stopped before suspend, and restarted after resume. This is done
using the pm_notifier mechanism.

Issue was found while doing suspend-to-ram on J721S2 EVM board with
omap-rng driver.

echo mem > /sys/power/state
[   27.922259] PM: suspend entry (deep)
[   27.927191] Filesystems sync: 0.000 seconds
[   27.933858] Freezing user space processes
[   27.939119] Freezing user space processes completed (elapsed 0.001 seconds)
[   27.946090] OOM killer disabled.
[   27.949315] Freezing remaining freezable tasks
[   27.954887] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[   27.963337] GFP mask restricted
[   27.967069] omap_rng 4e10000.rng: PM: calling platform_pm_suspend @ 195, parent: 4e00000.crypto
[   27.967072] mmcblk mmc1:9fb0: PM: calling mmc_bus_suspend @ 122, parent: mmc1
[   27.968636] mmcblk mmc1:9fb0: PM: mmc_bus_suspend returned 0 after 1546 usecs
[   27.975778] omap_rng 4e10000.rng: PM: platform_pm_suspend returned 0 after 3 usecs
...
[   33.510667] ti-sci 44083000.system-controller: PM: ti_sci_suspend_noirq returned 0 after 0 usecs
[   33.510671] SError Interrupt on CPU0, code 0x00000000bf000000 -- SError
[   33.510681] CPU: 0 UID: 0 PID: 132 Comm: hwrng Tainted: G   M    W           7.0.0-12695-g8923b7a6e11d #19 PREEMPT
[   33.510690] Tainted: [M]=MACHINE_CHECK, [W]=WARN
[   33.510693] Hardware name: Texas Instruments J721S2 EVM (DT)
[   33.510697] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   33.510701] pc : omap_rng_do_read+0x3c/0xe0
[   33.510709] lr : omap_rng_do_read+0x58/0xe0
[   33.510712] sp : ffff80008942be00
[   33.510713] x29: ffff80008942be00 x28: 0000000000000000 x27: 0000000000000000
[   33.510719] x26: 0000000000000010 x25: 0000000000000010 x24: ffff0008065644e8
[   33.510724] x23: ffff8000878b3370 x22: ffff00080148b2c0 x21: 0000000000000000
[   33.510728] x20: ffff000806564480 x19: 0000000000000064 x18: 0000000000000000
[   33.510732] x17: 6573752031207265 x16: 7466612030206465 x15: 6e72757465722071
[   33.510737] x14: ffff0008062c8080 x13: 000031702bc0da42 x12: 0000000000000001
[   33.510741] x11: 00000000000000c0 x10: 0000000000000b30 x9 : ffff80008942bc80
[   33.510745] x8 : ffff0008062c8b90 x7 : ffff000b7dfa34c0 x6 : 0000000805ca16c1
[   33.510749] x5 : 0000000000000000 x4 : ffff800080e17bfc x3 : ffff800087389c68
[   33.510753] x2 : 0000000000000000 x1 : 0000000000000010 x0 : 000000000000a7c6
[   33.510759] Kernel panic - not syncing: Asynchronous SError Interrupt
[   33.510762] CPU: 0 UID: 0 PID: 132 Comm: hwrng Tainted: G   M    W           7.0.0-12695-g8923b7a6e11d #19 PREEMPT
[   33.510767] Tainted: [M]=MACHINE_CHECK, [W]=WARN
[   33.510768] Hardware name: Texas Instruments J721S2 EVM (DT)
[   33.510770] Call trace:
[   33.510772]  show_stack+0x18/0x24 (C)
[   33.510780]  dump_stack_lvl+0x34/0x8c
[   33.510788]  dump_stack+0x18/0x24
[   33.510792]  vpanic+0x47c/0x4dc
[   33.510799]  do_panic_on_target_cpu+0x0/0x1c
[   33.510803]  add_taint+0x0/0xbc
[   33.510807]  arm64_serror_panic+0x70/0x80
[   33.510812]  do_serror+0x3c/0x70
[   33.510815]  el1h_64_error_handler+0x34/0x50
[   33.510823]  el1h_64_error+0x6c/0x70
[   33.510827]  omap_rng_do_read+0x3c/0xe0 (P)
[   33.510831]  hwrng_fillfn+0x98/0x330
[   33.510834]  kthread+0x130/0x13c
[   33.510845]  ret_from_fork+0x10/0x20
[   33.510850] SMP: stopping secondary CPUs
[   33.519442] Kernel Offset: disabled
[   33.519444] CPU features: 0x04000000,800a0008,00040001,0400421b
[   33.519448] Memory Limit: none
[   33.732904] ---[ end Kernel panic - not syncing: Asynchronous SError Interrupt ]---

Signed-off-by: Thomas Richard (TI) <thomas.richard@bootlin.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Thomas Richard (TI) 2026-08-04 12:01:09 +02:00 committed by Herbert Xu
parent b82f60be50
commit b1c0e12097
1 changed files with 86 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

101
drivers/char/hw_random/core.c
View File

@ -17,14 +17,17 @@
#include <linux/hw_random.h>
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/lockdep.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/random.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/suspend.h>
#include <linux/sysfs.h>
#include <linux/uaccess.h>
#include <linux/workqueue.h>
@ -45,6 +48,8 @@ static DEFINE_MUTEX(rng_mutex);
static DEFINE_MUTEX(reading_mutex);
static int data_avail;
static u8 *rng_buffer, *rng_fillbuf;
/* Set to true during suspend-resume by PM notifier, protected by rng_mutex */
static bool hwrng_fillfn_stopped;
static unsigned short current_quality;
static unsigned short default_quality = 1024; /* default to maximum */
@ -57,6 +62,8 @@ MODULE_PARM_DESC(default_quality,
static int hwrng_init(struct hwrng *rng);
static int hwrng_fillfn(void *unused);
static void hwrng_start_hwrng_fillfn(void);
static void hwrng_stop_hwrng_fillfn(void);
static size_t rng_buffer_size(void)
{
@ -114,13 +121,7 @@ static int set_current_rng(struct hwrng *rng)
}
/* if necessary, start hwrng thread */
if (!hwrng_fill) {
hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
if (IS_ERR(hwrng_fill)) {
pr_err("hwrng_fill thread creation failed\n");
hwrng_fill = NULL;
}
}
hwrng_start_hwrng_fillfn();
return 0;
}
@ -137,10 +138,7 @@ static void drop_current_rng(void)
RCU_INIT_POINTER(current_rng, NULL);
synchronize_rcu();
if (hwrng_fill) {
kthread_stop(hwrng_fill);
hwrng_fill = NULL;
}
hwrng_stop_hwrng_fillfn();
/* decrease last reference for triggering the cleanup */
kref_put(&rng->ref, cleanup_rng);
@ -506,6 +504,36 @@ static struct attribute *rng_dev_attrs[] = {
ATTRIBUTE_GROUPS(rng_dev);
static void hwrng_start_hwrng_fillfn(void)
{
lockdep_assert_held(&rng_mutex);
/*
* PM notifier stopped the hwrng_fillfn kthread, prevent userspace to
* restart it until kernel freezes threads.
*/
if (hwrng_fillfn_stopped)
return;
if (!hwrng_fill) {
hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
if (IS_ERR(hwrng_fill)) {
pr_err("hwrng_fill thread creation failed\n");
hwrng_fill = NULL;
}
}
}
static void hwrng_stop_hwrng_fillfn(void)
{
lockdep_assert_held(&rng_mutex);
if (hwrng_fill) {
kthread_stop(hwrng_fill);
hwrng_fill = NULL;
}
}
static int hwrng_fillfn(void *unused)
{
size_t entropy, entropy_credit = 0; /* in 1/1024 of a bit */
@ -559,6 +587,37 @@ static int hwrng_fillfn(void *unused)
return 0;
}
static int hwrng_pm_notifier(struct notifier_block *nb, unsigned long action,
void *data)
{
switch (action) {
case PM_SUSPEND_PREPARE:
case PM_HIBERNATION_PREPARE:
case PM_RESTORE_PREPARE:
mutex_lock(&rng_mutex);
hwrng_stop_hwrng_fillfn();
hwrng_fillfn_stopped = true;
mutex_unlock(&rng_mutex);
break;
case PM_POST_SUSPEND:
case PM_POST_HIBERNATION:
case PM_POST_RESTORE:
mutex_lock(&rng_mutex);
hwrng_fillfn_stopped = false;
if (rcu_access_pointer(current_rng))
hwrng_start_hwrng_fillfn();
mutex_unlock(&rng_mutex);
break;
}
return NOTIFY_DONE;
}
static struct notifier_block hwrng_pm_nb = {
.notifier_call = hwrng_pm_notifier,
};
int hwrng_register(struct hwrng *rng)
{
int err = -EINVAL;
@ -707,10 +766,20 @@ static int __init hwrng_modinit(void)
}
ret = misc_register(&rng_miscdev);
if (ret) {
kfree(rng_fillbuf);
kfree(rng_buffer);
}
if (ret)
goto misc_err;
ret = register_pm_notifier(&hwrng_pm_nb);
if (ret)
goto pm_err;
return 0;
pm_err:
misc_deregister(&rng_miscdev);
misc_err:
kfree(rng_fillbuf);
kfree(rng_buffer);
return ret;
}
@ -723,6 +792,8 @@ static void __exit hwrng_modexit(void)
kfree(rng_fillbuf);
mutex_unlock(&rng_mutex);
unregister_pm_notifier(&hwrng_pm_nb);
misc_deregister(&rng_miscdev);
}