Revision e2093926a098a8ccf0f1d10f6df8dad452cb28d3 authored by Ross Zwisler on 02 June 2017, 21:46:37 UTC, committed by Linus Torvalds on 02 June 2017, 22:07:37 UTC
We currently have two related PMD vs PTE races in the DAX code. These can both be easily triggered by having two threads reading and writing simultaneously to the same private mapping, with the key being that private mapping reads can be handled with PMDs but private mapping writes are always handled with PTEs so that we can COW. Here is the first race: CPU 0 CPU 1 (private mapping write) __handle_mm_fault() create_huge_pmd() - FALLBACK handle_pte_fault() passes check for pmd_devmap() (private mapping read) __handle_mm_fault() create_huge_pmd() dax_iomap_pmd_fault() inserts PMD dax_iomap_pte_fault() does a PTE fault, but we already have a DAX PMD installed in our page tables at this spot. Here's the second race: CPU 0 CPU 1 (private mapping read) __handle_mm_fault() passes check for pmd_none() create_huge_pmd() dax_iomap_pmd_fault() inserts PMD (private mapping write) __handle_mm_fault() create_huge_pmd() - FALLBACK (private mapping read) __handle_mm_fault() passes check for pmd_none() create_huge_pmd() handle_pte_fault() dax_iomap_pte_fault() inserts PTE dax_iomap_pmd_fault() inserts PMD, but we already have a PTE at this spot. The core of the issue is that while there is isolation between faults to the same range in the DAX fault handlers via our DAX entry locking, there is no isolation between faults in the code in mm/memory.c. This means for instance that this code in __handle_mm_fault() can run: if (pmd_none(*vmf.pmd) && transparent_hugepage_enabled(vma)) { ret = create_huge_pmd(&vmf); But by the time we actually get to run the fault handler called by create_huge_pmd(), the PMD is no longer pmd_none() because a racing PTE fault has installed a normal PMD here as a parent. This is the cause of the 2nd race. The first race is similar - there is the following check in handle_pte_fault(): } else { /* See comment in pte_alloc_one_map() */ if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd)) return 0; So if a pmd_devmap() PMD (a DAX PMD) has been installed at vmf->pmd, we will bail and retry the fault. This is correct, but there is nothing preventing the PMD from being installed after this check but before we actually get to the DAX PTE fault handlers. In my testing these races result in the following types of errors: BUG: Bad rss-counter state mm:ffff8800a817d280 idx:1 val:1 BUG: non-zero nr_ptes on freeing mm: 15 Fix this issue by having the DAX fault handlers verify that it is safe to continue their fault after they have taken an entry lock to block other racing faults. [ross.zwisler@linux.intel.com: improve fix for colliding PMD & PTE entries] Link: http://lkml.kernel.org/r/20170526195932.32178-1-ross.zwisler@linux.intel.com Link: http://lkml.kernel.org/r/20170522215749.23516-2-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> Reported-by: Pawel Lebioda <pawel.lebioda@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: "Darrick J. Wong" <darrick.wong@oracle.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: Pawel Lebioda <pawel.lebioda@intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Xiong Zhou <xzhou@redhat.com> Cc: Eryu Guan <eguan@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent d0f0931
mac_hid.c
/*
* drivers/macintosh/mac_hid.c
*
* HID support stuff for Macintosh computers.
*
* Copyright (C) 2000 Franz Sirl.
*
* This file will soon be removed in favor of an uinput userspace tool.
*/
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/sysctl.h>
#include <linux/input.h>
#include <linux/module.h>
#include <linux/slab.h>
MODULE_LICENSE("GPL");
static int mouse_emulate_buttons;
static int mouse_button2_keycode = KEY_RIGHTCTRL; /* right control key */
static int mouse_button3_keycode = KEY_RIGHTALT; /* right option key */
static struct input_dev *mac_hid_emumouse_dev;
static DEFINE_MUTEX(mac_hid_emumouse_mutex);
static int mac_hid_create_emumouse(void)
{
static struct lock_class_key mac_hid_emumouse_dev_event_class;
static struct lock_class_key mac_hid_emumouse_dev_mutex_class;
int err;
mac_hid_emumouse_dev = input_allocate_device();
if (!mac_hid_emumouse_dev)
return -ENOMEM;
lockdep_set_class(&mac_hid_emumouse_dev->event_lock,
&mac_hid_emumouse_dev_event_class);
lockdep_set_class(&mac_hid_emumouse_dev->mutex,
&mac_hid_emumouse_dev_mutex_class);
mac_hid_emumouse_dev->name = "Macintosh mouse button emulation";
mac_hid_emumouse_dev->id.bustype = BUS_ADB;
mac_hid_emumouse_dev->id.vendor = 0x0001;
mac_hid_emumouse_dev->id.product = 0x0001;
mac_hid_emumouse_dev->id.version = 0x0100;
mac_hid_emumouse_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);
mac_hid_emumouse_dev->keybit[BIT_WORD(BTN_MOUSE)] =
BIT_MASK(BTN_LEFT) | BIT_MASK(BTN_MIDDLE) | BIT_MASK(BTN_RIGHT);
mac_hid_emumouse_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y);
err = input_register_device(mac_hid_emumouse_dev);
if (err) {
input_free_device(mac_hid_emumouse_dev);
mac_hid_emumouse_dev = NULL;
return err;
}
return 0;
}
static void mac_hid_destroy_emumouse(void)
{
input_unregister_device(mac_hid_emumouse_dev);
mac_hid_emumouse_dev = NULL;
}
static bool mac_hid_emumouse_filter(struct input_handle *handle,
unsigned int type, unsigned int code,
int value)
{
unsigned int btn;
if (type != EV_KEY)
return false;
if (code == mouse_button2_keycode)
btn = BTN_MIDDLE;
else if (code == mouse_button3_keycode)
btn = BTN_RIGHT;
else
return false;
input_report_key(mac_hid_emumouse_dev, btn, value);
input_sync(mac_hid_emumouse_dev);
return true;
}
static int mac_hid_emumouse_connect(struct input_handler *handler,
struct input_dev *dev,
const struct input_device_id *id)
{
struct input_handle *handle;
int error;
/* Don't bind to ourselves */
if (dev == mac_hid_emumouse_dev)
return -ENODEV;
handle = kzalloc(sizeof(struct input_handle), GFP_KERNEL);
if (!handle)
return -ENOMEM;
handle->dev = dev;
handle->handler = handler;
handle->name = "mac-button-emul";
error = input_register_handle(handle);
if (error) {
printk(KERN_ERR
"mac_hid: Failed to register button emulation handle, "
"error %d\n", error);
goto err_free;
}
error = input_open_device(handle);
if (error) {
printk(KERN_ERR
"mac_hid: Failed to open input device, error %d\n",
error);
goto err_unregister;
}
return 0;
err_unregister:
input_unregister_handle(handle);
err_free:
kfree(handle);
return error;
}
static void mac_hid_emumouse_disconnect(struct input_handle *handle)
{
input_close_device(handle);
input_unregister_handle(handle);
kfree(handle);
}
static const struct input_device_id mac_hid_emumouse_ids[] = {
{
.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
.evbit = { BIT_MASK(EV_KEY) },
},
{ },
};
MODULE_DEVICE_TABLE(input, mac_hid_emumouse_ids);
static struct input_handler mac_hid_emumouse_handler = {
.filter = mac_hid_emumouse_filter,
.connect = mac_hid_emumouse_connect,
.disconnect = mac_hid_emumouse_disconnect,
.name = "mac-button-emul",
.id_table = mac_hid_emumouse_ids,
};
static int mac_hid_start_emulation(void)
{
int err;
err = mac_hid_create_emumouse();
if (err)
return err;
err = input_register_handler(&mac_hid_emumouse_handler);
if (err) {
mac_hid_destroy_emumouse();
return err;
}
return 0;
}
static void mac_hid_stop_emulation(void)
{
input_unregister_handler(&mac_hid_emumouse_handler);
mac_hid_destroy_emumouse();
}
static int mac_hid_toggle_emumouse(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int *valp = table->data;
int old_val = *valp;
int rc;
rc = mutex_lock_killable(&mac_hid_emumouse_mutex);
if (rc)
return rc;
rc = proc_dointvec(table, write, buffer, lenp, ppos);
if (rc == 0 && write && *valp != old_val) {
if (*valp == 1)
rc = mac_hid_start_emulation();
else if (*valp == 0)
mac_hid_stop_emulation();
else
rc = -EINVAL;
}
/* Restore the old value in case of error */
if (rc)
*valp = old_val;
mutex_unlock(&mac_hid_emumouse_mutex);
return rc;
}
/* file(s) in /proc/sys/dev/mac_hid */
static struct ctl_table mac_hid_files[] = {
{
.procname = "mouse_button_emulation",
.data = &mouse_emulate_buttons,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = mac_hid_toggle_emumouse,
},
{
.procname = "mouse_button2_keycode",
.data = &mouse_button2_keycode,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
{
.procname = "mouse_button3_keycode",
.data = &mouse_button3_keycode,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
{ }
};
/* dir in /proc/sys/dev */
static struct ctl_table mac_hid_dir[] = {
{
.procname = "mac_hid",
.maxlen = 0,
.mode = 0555,
.child = mac_hid_files,
},
{ }
};
/* /proc/sys/dev itself, in case that is not there yet */
static struct ctl_table mac_hid_root_dir[] = {
{
.procname = "dev",
.maxlen = 0,
.mode = 0555,
.child = mac_hid_dir,
},
{ }
};
static struct ctl_table_header *mac_hid_sysctl_header;
static int __init mac_hid_init(void)
{
mac_hid_sysctl_header = register_sysctl_table(mac_hid_root_dir);
if (!mac_hid_sysctl_header)
return -ENOMEM;
return 0;
}
module_init(mac_hid_init);
static void __exit mac_hid_exit(void)
{
unregister_sysctl_table(mac_hid_sysctl_header);
if (mouse_emulate_buttons)
mac_hid_stop_emulation();
}
module_exit(mac_hid_exit);
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