From: Greg Kroah-Hartman gregkh@linuxfoundation.org
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 calles 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(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 7966c9a1c163..388299525f3c 100644 --- 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
On 7/12/25 01:03, Hauke Mehrtens wrote:
From: Greg Kroah-Hartman gregkh@linuxfoundation.org
Sorry this has the wrong from tag, will send a new patch.
Hauke>
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 calles 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(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 7966c9a1c163..388299525f3c 100644 --- 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
On Sat, 12 Jul 2025 01:06:07 +0200 Hauke Mehrtens hauke@hauke-m.de wrote:
On 7/12/25 01:03, Hauke Mehrtens wrote:
From: Greg Kroah-Hartman gregkh@linuxfoundation.org
Sorry this has the wrong from tag, will send a new patch.
Hauke>
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 calles 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 bet it doesn't - it is likely to fail somewhere else instead. While 20 is probably too low, the real issue seems to be that the hotplug notifications need rate limiting.
David
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(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 7966c9a1c163..388299525f3c 100644 --- 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
linux-stable-mirror@lists.linaro.org
-
David Laight -
Hauke Mehrtens