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kernel: Fix boot of amrsr target in qemu

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The bootup of the armsr target sometimes failed like this:
```
[    0.762283] NET: Registered PF_INET6 protocol family
[    0.791987] workqueue: Failed to create a worker thread: -EAGAIN
[    0.801986] workqueue: Failed to create a rescuer kthread for wq "mld": -EAGAIN
[    0.964017] NET: Unregistered PF_INET6 protocol family
```

Increase the maximum number of threads the kernel allows.

Link: https://github.com/openwrt/openwrt/pull/19376
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
This commit is contained in:
Hauke Mehrtens 2025-07-12 00:55:38 +02:00
parent 01a9a27dfa
commit c5330bdf7e
2 changed files with 74 additions and 0 deletions
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37
target/linux/generic/pending-6.12/250-kernel-fork-Increase-minimum-number-of-allowed-threa.patch Normal file
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@ -0,0 +1,37 @@
From a22c4c7bbfad3e93e717e16f6faf343259add27a Mon Sep 17 00:00:00 2001
From: Hauke Mehrtens <hauke@hauke-m.de>
Date: Fri, 27 Jun 2025 11:09:04 +0100
Subject: [PATCH v2] kernel/fork: Increase minimum number of allowed threads
A modern Linux system creates much more than 20 threads at bootup.
When I booted up OpenWrt in qemu the system sometimes failed to boot up
when it wanted to create the 419th thread. The VM had 128MB RAM and the
calculation in set_max_threads() calculated that max_threads should be
set to 419. When the system booted up it tried to notify the user space
about every device it created because CONFIG_UEVENT_HELPER was set and
used. I counted 1299 calls to call_usermodehelper_setup(), all of
them try to create a new thread and call the userspace hotplug script in
it.
This fixes bootup of Linux on systems with low memory.
I saw the problem with qemu 10.0.2 using these commands:
qemu-system-aarch64 -machine virt -cpu cortex-a57 -nographic
Cc: stable@vger.kernel.org
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
---
kernel/fork.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -123,7 +123,7 @@
/*
* Minimum number of threads to boot the kernel
*/
-#define MIN_THREADS 20
+#define MIN_THREADS 600
/*
* Maximum number of threads

37
target/linux/generic/pending-6.6/250-kernel-fork-Increase-minimum-number-of-allowed-threa.patch Normal file
View file

@ -0,0 +1,37 @@
From a22c4c7bbfad3e93e717e16f6faf343259add27a Mon Sep 17 00:00:00 2001
From: Hauke Mehrtens <hauke@hauke-m.de>
Date: Fri, 27 Jun 2025 11:09:04 +0100
Subject: [PATCH v2] kernel/fork: Increase minimum number of allowed threads
A modern Linux system creates much more than 20 threads at bootup.
When I booted up OpenWrt in qemu the system sometimes failed to boot up
when it wanted to create the 419th thread. The VM had 128MB RAM and the
calculation in set_max_threads() calculated that max_threads should be
set to 419. When the system booted up it tried to notify the user space
about every device it created because CONFIG_UEVENT_HELPER was set and
used. I counted 1299 calls to call_usermodehelper_setup(), all of
them try to create a new thread and call the userspace hotplug script in
it.
This fixes bootup of Linux on systems with low memory.
I saw the problem with qemu 10.0.2 using these commands:
qemu-system-aarch64 -machine virt -cpu cortex-a57 -nographic
Cc: stable@vger.kernel.org
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
---
kernel/fork.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -115,7 +115,7 @@
/*
* Minimum number of threads to boot the kernel
*/
-#define MIN_THREADS 20
+#define MIN_THREADS 600
/*
* Maximum number of threads