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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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e84276c8dd
[ Upstream commit76d62f24db] Wei Wang reported seeing priority inversion caused latencies caused by contention on pmsg_lock, and suggested it be switched to a rt_mutex. I was initially hesitant this would help, as the tasks in that trace all seemed to be SCHED_NORMAL, so the benefit would be limited to only nice boosting. However, another similar issue was raised where the priority inversion was seen did involve a blocked RT task so it is clear this would be helpful in that case. Cc: Wei Wang <wvw@google.com> Cc: Midas Chien<midaschieh@google.com> Cc: Connor O'Brien <connoro@google.com> Cc: Kees Cook <keescook@chromium.org> Cc: Anton Vorontsov <anton@enomsg.org> Cc: Colin Cross <ccross@android.com> Cc: Tony Luck <tony.luck@intel.com> Cc: kernel-team@android.com Fixes:9d5438f462("pstore: Add pmsg - user-space accessible pstore object") Reported-by: Wei Wang <wvw@google.com> Signed-off-by: John Stultz <jstultz@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20221214231834.3711880-1-jstultz@google.com Signed-off-by: Sasha Levin <sashal@kernel.org>
95 lines
2 KiB
C
95 lines
2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright 2014 Google, Inc.
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*/
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#include <linux/cdev.h>
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#include <linux/device.h>
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#include <linux/fs.h>
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#include <linux/uaccess.h>
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#include <linux/rtmutex.h>
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#include "internal.h"
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static DEFINE_RT_MUTEX(pmsg_lock);
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static ssize_t write_pmsg(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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{
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struct pstore_record record;
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int ret;
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if (!count)
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return 0;
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pstore_record_init(&record, psinfo);
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record.type = PSTORE_TYPE_PMSG;
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record.size = count;
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/* check outside lock, page in any data. write_user also checks */
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if (!access_ok(buf, count))
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return -EFAULT;
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rt_mutex_lock(&pmsg_lock);
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ret = psinfo->write_user(&record, buf);
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rt_mutex_unlock(&pmsg_lock);
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return ret ? ret : count;
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}
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static const struct file_operations pmsg_fops = {
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.owner = THIS_MODULE,
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.llseek = noop_llseek,
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.write = write_pmsg,
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};
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static struct class *pmsg_class;
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static int pmsg_major;
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#define PMSG_NAME "pmsg"
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#undef pr_fmt
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#define pr_fmt(fmt) PMSG_NAME ": " fmt
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static char *pmsg_devnode(struct device *dev, umode_t *mode)
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{
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if (mode)
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*mode = 0220;
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return NULL;
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}
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void pstore_register_pmsg(void)
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{
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struct device *pmsg_device;
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pmsg_major = register_chrdev(0, PMSG_NAME, &pmsg_fops);
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if (pmsg_major < 0) {
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pr_err("register_chrdev failed\n");
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goto err;
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}
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pmsg_class = class_create(THIS_MODULE, PMSG_NAME);
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if (IS_ERR(pmsg_class)) {
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pr_err("device class file already in use\n");
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goto err_class;
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}
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pmsg_class->devnode = pmsg_devnode;
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pmsg_device = device_create(pmsg_class, NULL, MKDEV(pmsg_major, 0),
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NULL, "%s%d", PMSG_NAME, 0);
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if (IS_ERR(pmsg_device)) {
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pr_err("failed to create device\n");
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goto err_device;
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}
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return;
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err_device:
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class_destroy(pmsg_class);
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err_class:
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unregister_chrdev(pmsg_major, PMSG_NAME);
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err:
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return;
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}
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void pstore_unregister_pmsg(void)
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{
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device_destroy(pmsg_class, MKDEV(pmsg_major, 0));
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class_destroy(pmsg_class);
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unregister_chrdev(pmsg_major, PMSG_NAME);
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}
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