The patch below does not apply to the 6.17-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.17.y
git checkout FETCH_HEAD
git cherry-pick -x 201c53c687f2b55a7cc6d9f4000af4797860174b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101642-jumble-hatchback-ff0f@gregkh' --subject-prefix 'PATCH 6.17.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 201c53c687f2b55a7cc6d9f4000af4797860174b Mon Sep 17 00:00:00 2001
From: Kuen-Han Tsai <khtsai(a)google.com>
Date: Tue, 16 Sep 2025 16:21:33 +0800
Subject: [PATCH] usb: gadget: Introduce free_usb_request helper
Introduce the free_usb_request() function that frees both the request's
buffer and the request itself.
This function serves as the cleanup callback for DEFINE_FREE() to enable
automatic, scope-based cleanup for usb_request pointers.
Signed-off-by: Kuen-Han Tsai <khtsai(a)google.com>
Link: https://lore.kernel.org/r/20250916-ready-v1-2-4997bf277548@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org>
Link: https://lore.kernel.org/r/20250916-ready-v1-2-4997bf277548@google.com
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 0f2079476088..3aaf19e77558 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -15,6 +15,7 @@
#ifndef __LINUX_USB_GADGET_H
#define __LINUX_USB_GADGET_H
+#include <linux/cleanup.h>
#include <linux/configfs.h>
#include <linux/device.h>
#include <linux/errno.h>
@@ -293,6 +294,28 @@ static inline void usb_ep_fifo_flush(struct usb_ep *ep)
/*-------------------------------------------------------------------------*/
+/**
+ * free_usb_request - frees a usb_request object and its buffer
+ * @req: the request being freed
+ *
+ * This helper function frees both the request's buffer and the request object
+ * itself by calling usb_ep_free_request(). Its signature is designed to be used
+ * with DEFINE_FREE() to enable automatic, scope-based cleanup for usb_request
+ * pointers.
+ */
+static inline void free_usb_request(struct usb_request *req)
+{
+ if (!req)
+ return;
+
+ kfree(req->buf);
+ usb_ep_free_request(req->ep, req);
+}
+
+DEFINE_FREE(free_usb_request, struct usb_request *, free_usb_request(_T))
+
+/*-------------------------------------------------------------------------*/
+
struct usb_dcd_config_params {
__u8 bU1devExitLat; /* U1 Device exit Latency */
#define USB_DEFAULT_U1_DEV_EXIT_LAT 0x01 /* Less then 1 microsec */
Hello.
We have observed a huge latency increase using `fork()` after ingesting the CVE-2025-38085 fix which leads to the commit `1013af4f585f: mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race`. On large machines with 1.5TB of memory with 196 cores, we identified mmapping of 1.2TB of shared memory and forking itself dozens or hundreds of times we see a increase of execution times of a factor of 4. The reproducer is at the end of the email.
Comparing the a kernel without this patch with a kernel with this patch applied when spawning 1000 children we see those execution times:
Patched kernel:
$ time make stress
...
real 0m11.275s
user 0m0.177s
sys 0m23.905s
Original kernel :
$ time make stress
...real 0m2.475s
user 0m1.398s
sys 0m2.501s
The patch in question: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id…
My observation/assumption is:
each child touches 100 random pages and despawns
on each despawn `huge_pmd_unshare()` is called
each call to `huge_pmd_unshare()` syncrhonizes all threads using `tlb_remove_table_sync_one()` leading to the regression
I'm happy to provide more information.
Thank you
Stanislav Uschakow
=== Reproducer ===
Setup:
#!/bin/bash
echo "Setting up hugepages for reproduction..."
# hugepages (1.2TB / 2MB = 614400 pages)
REQUIRED_PAGES=614400
# Check current hugepage allocation
CURRENT_PAGES=$(cat /proc/sys/vm/nr_hugepages)
echo "Current hugepages: $CURRENT_PAGES"
if [ "$CURRENT_PAGES" -lt "$REQUIRED_PAGES" ]; then
echo "Allocating $REQUIRED_PAGES hugepages..."
echo $REQUIRED_PAGES | sudo tee /proc/sys/vm/nr_hugepages
ALLOCATED=$(cat /proc/sys/vm/nr_hugepages)
echo "Allocated hugepages: $ALLOCATED"
if [ "$ALLOCATED" -lt "$REQUIRED_PAGES" ]; then
echo "Warning: Could not allocate all required hugepages"
echo "Available: $ALLOCATED, Required: $REQUIRED_PAGES"
fi
fi
echo never | sudo tee /sys/kernel/mm/transparent_hugepage/enabled
echo -e "\nHugepage information:"
cat /proc/meminfo | grep -i huge
echo -e "\nSetup complete. You can now run the reproduction test."
Makefile:
CXX = gcc
CXXFLAGS = -O2 -Wall
TARGET = hugepage_repro
SOURCE = hugepage_repro.c
$(TARGET): $(SOURCE)
$(CXX) $(CXXFLAGS) -o $(TARGET) $(SOURCE)
clean:
rm -f $(TARGET)
setup:
chmod +x setup_hugepages.sh
./setup_hugepages.sh
test: $(TARGET)
./$(TARGET) 20 3
stress: $(TARGET)
./$(TARGET) 1000 1
.PHONY: clean setup test stress
hugepage_repro.c:
#include <sys/mman.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <stdio.h>
#define HUGEPAGE_SIZE (2 * 1024 * 1024) // 2MB
#define TOTAL_SIZE (1200ULL * 1024 * 1024 * 1024) // 1.2TB
#define NUM_HUGEPAGES (TOTAL_SIZE / HUGEPAGE_SIZE)
void* create_hugepage_mapping() {
void* addr = mmap(NULL, TOTAL_SIZE, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
if (addr == MAP_FAILED) {
perror("mmap hugepages failed");
exit(1);
}
return addr;
}
void touch_random_pages(void* addr, int num_touches) {
char* base = (char*)addr;
for (int i = 0; i < num_touches; ++i) {
size_t offset = (rand() % NUM_HUGEPAGES) * HUGEPAGE_SIZE;
volatile char val = base[offset];
(void)val;
}
}
void child_process(void* shared_mem, int child_id) {
struct timespec start, end;
clock_gettime(CLOCK_MONOTONIC, &start);
touch_random_pages(shared_mem, 100);
clock_gettime(CLOCK_MONOTONIC, &end);
long duration = (end.tv_sec - start.tv_sec) * 1000000 +
(end.tv_nsec - start.tv_nsec) / 1000;
printf("Child %d completed in %ld μs\n", child_id, duration);
}
int main(int argc, char* argv[]) {
int num_processes = argc > 1 ? atoi(argv[1]) : 50;
int iterations = argc > 2 ? atoi(argv[2]) : 5;
printf("Creating %lluGB hugepage mapping...\n", TOTAL_SIZE / (1024*1024*1024));
void* shared_mem = create_hugepage_mapping();
for (int iter = 0; iter < iterations; ++iter) {
printf("\nIteration %d: Forking %d processes\n", iter + 1, num_processes);
pid_t children[num_processes];
struct timespec iter_start, iter_end;
clock_gettime(CLOCK_MONOTONIC, &iter_start);
for (int i = 0; i < num_processes; ++i) {
pid_t pid = fork();
if (pid == 0) {
child_process(shared_mem, i);
exit(0);
} else if (pid > 0) {
children[i] = pid;
}
}
for (int i = 0; i < num_processes; ++i) {
waitpid(children[i], NULL, 0);
}
clock_gettime(CLOCK_MONOTONIC, &iter_end);
long iter_duration = (iter_end.tv_sec - iter_start.tv_sec) * 1000 +
(iter_end.tv_nsec - iter_start.tv_nsec) / 1000000;
printf("Iteration completed in %ld ms\n", iter_duration);
}
munmap(shared_mem, TOTAL_SIZE);
return 0;
}
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