Revision e91467ecd1ef381377fd327c0ded922835ec52ab authored by Christian Borntraeger on 05 August 2006, 19:13:52 UTC, committed by Linus Torvalds on 06 August 2006, 15:57:46 UTC
This patch adds a barrier() in futex unqueue_me to avoid aliasing of two
pointers.
On my s390x system I saw the following oops:
Unable to handle kernel pointer dereference at virtual kernel address
0000000000000000
Oops: 0004 [#1]
CPU: 0 Not tainted
Process mytool (pid: 13613, task: 000000003ecb6ac0, ksp: 00000000366bdbd8)
Krnl PSW : 0704d00180000000 00000000003c9ac2 (_spin_lock+0xe/0x30)
Krnl GPRS: 00000000ffffffff 000000003ecb6ac0 0000000000000000 0700000000000000
0000000000000000 0000000000000000 000001fe00002028 00000000000c091f
000001fe00002054 000001fe00002054 0000000000000000 00000000366bddc0
00000000005ef8c0 00000000003d00e8 0000000000144f91 00000000366bdcb8
Krnl Code: ba 4e 20 00 12 44 b9 16 00 3e a7 84 00 08 e3 e0 f0 88 00 04
Call Trace:
([<0000000000144f90>] unqueue_me+0x40/0xe4)
[<0000000000145a0c>] do_futex+0x33c/0xc40
[<000000000014643e>] sys_futex+0x12e/0x144
[<000000000010bb00>] sysc_noemu+0x10/0x16
[<000002000003741c>] 0x2000003741c
The code in question is:
static int unqueue_me(struct futex_q *q)
{
int ret = 0;
spinlock_t *lock_ptr;
/* In the common case we don't take the spinlock, which is nice. */
retry:
lock_ptr = q->lock_ptr;
if (lock_ptr != 0) {
spin_lock(lock_ptr);
/*
* q->lock_ptr can change between reading it and
* spin_lock(), causing us to take the wrong lock. This
* corrects the race condition.
[...]
and my compiler (gcc 4.1.0) makes the following out of it:
00000000000003c8 <unqueue_me>:
3c8: eb bf f0 70 00 24 stmg %r11,%r15,112(%r15)
3ce: c0 d0 00 00 00 00 larl %r13,3ce <unqueue_me+0x6>
3d0: R_390_PC32DBL .rodata+0x2a
3d4: a7 f1 1e 00 tml %r15,7680
3d8: a7 84 00 01 je 3da <unqueue_me+0x12>
3dc: b9 04 00 ef lgr %r14,%r15
3e0: a7 fb ff d0 aghi %r15,-48
3e4: b9 04 00 b2 lgr %r11,%r2
3e8: e3 e0 f0 98 00 24 stg %r14,152(%r15)
3ee: e3 c0 b0 28 00 04 lg %r12,40(%r11)
/* write q->lock_ptr in r12 */
3f4: b9 02 00 cc ltgr %r12,%r12
3f8: a7 84 00 4b je 48e <unqueue_me+0xc6>
/* if r12 is zero then jump over the code.... */
3fc: e3 20 b0 28 00 04 lg %r2,40(%r11)
/* write q->lock_ptr in r2 */
402: c0 e5 00 00 00 00 brasl %r14,402 <unqueue_me+0x3a>
404: R_390_PC32DBL _spin_lock+0x2
/* use r2 as parameter for spin_lock */
So the code becomes more or less:
if (q->lock_ptr != 0) spin_lock(q->lock_ptr)
instead of
if (lock_ptr != 0) spin_lock(lock_ptr)
Which caused the oops from above.
After adding a barrier gcc creates code without this problem:
[...] (the same)
3ee: e3 c0 b0 28 00 04 lg %r12,40(%r11)
3f4: b9 02 00 cc ltgr %r12,%r12
3f8: b9 04 00 2c lgr %r2,%r12
3fc: a7 84 00 48 je 48c <unqueue_me+0xc4>
400: c0 e5 00 00 00 00 brasl %r14,400 <unqueue_me+0x38>
402: R_390_PC32DBL _spin_lock+0x2
As a general note, this code of unqueue_me seems a bit fishy. The retry logic
of unqueue_me only works if we can guarantee, that the original value of
q->lock_ptr is always a spinlock (Otherwise we overwrite kernel memory). We
know that q->lock_ptr can change. I dont know what happens with the original
spinlock, as I am not an expert with the futex code.
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@timesys.com>
Signed-off-by: Christian Borntraeger <borntrae@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent 72f0b4e
adlib.c
/*
* AdLib FM card driver.
*/
#include <sound/driver.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <sound/core.h>
#include <sound/initval.h>
#include <sound/opl3.h>
#define CRD_NAME "AdLib FM"
#define DRV_NAME "snd_adlib"
MODULE_DESCRIPTION(CRD_NAME);
MODULE_AUTHOR("Rene Herman");
MODULE_LICENSE("GPL");
static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE;
static long port[SNDRV_CARDS] = SNDRV_DEFAULT_PORT;
module_param_array(index, int, NULL, 0444);
MODULE_PARM_DESC(index, "Index value for " CRD_NAME " soundcard.");
module_param_array(id, charp, NULL, 0444);
MODULE_PARM_DESC(id, "ID string for " CRD_NAME " soundcard.");
module_param_array(enable, bool, NULL, 0444);
MODULE_PARM_DESC(enable, "Enable " CRD_NAME " soundcard.");
module_param_array(port, long, NULL, 0444);
MODULE_PARM_DESC(port, "Port # for " CRD_NAME " driver.");
static struct platform_device *devices[SNDRV_CARDS];
static void snd_adlib_free(struct snd_card *card)
{
release_and_free_resource(card->private_data);
}
static int __devinit snd_adlib_probe(struct platform_device *device)
{
struct snd_card *card;
struct snd_opl3 *opl3;
int error, i = device->id;
if (port[i] == SNDRV_AUTO_PORT) {
snd_printk(KERN_ERR DRV_NAME ": please specify port\n");
error = -EINVAL;
goto out0;
}
card = snd_card_new(index[i], id[i], THIS_MODULE, 0);
if (!card) {
snd_printk(KERN_ERR DRV_NAME ": could not create card\n");
error = -EINVAL;
goto out0;
}
card->private_data = request_region(port[i], 4, CRD_NAME);
if (!card->private_data) {
snd_printk(KERN_ERR DRV_NAME ": could not grab ports\n");
error = -EBUSY;
goto out1;
}
card->private_free = snd_adlib_free;
error = snd_opl3_create(card, port[i], port[i] + 2, OPL3_HW_AUTO, 1, &opl3);
if (error < 0) {
snd_printk(KERN_ERR DRV_NAME ": could not create OPL\n");
goto out1;
}
error = snd_opl3_hwdep_new(opl3, 0, 0, NULL);
if (error < 0) {
snd_printk(KERN_ERR DRV_NAME ": could not create FM\n");
goto out1;
}
strcpy(card->driver, DRV_NAME);
strcpy(card->shortname, CRD_NAME);
sprintf(card->longname, CRD_NAME " at %#lx", port[i]);
snd_card_set_dev(card, &device->dev);
error = snd_card_register(card);
if (error < 0) {
snd_printk(KERN_ERR DRV_NAME ": could not register card\n");
goto out1;
}
platform_set_drvdata(device, card);
return 0;
out1: snd_card_free(card);
out0: return error;
}
static int __devexit snd_adlib_remove(struct platform_device *device)
{
snd_card_free(platform_get_drvdata(device));
platform_set_drvdata(device, NULL);
return 0;
}
static struct platform_driver snd_adlib_driver = {
.probe = snd_adlib_probe,
.remove = __devexit_p(snd_adlib_remove),
.driver = {
.name = DRV_NAME
}
};
static int __init alsa_card_adlib_init(void)
{
int i, cards;
if (platform_driver_register(&snd_adlib_driver) < 0) {
snd_printk(KERN_ERR DRV_NAME ": could not register driver\n");
return -ENODEV;
}
for (cards = 0, i = 0; i < SNDRV_CARDS; i++) {
struct platform_device *device;
if (!enable[i])
continue;
device = platform_device_register_simple(DRV_NAME, i, NULL, 0);
if (IS_ERR(device))
continue;
if (!platform_get_drvdata(device)) {
platform_device_unregister(device);
continue;
}
devices[i] = device;
cards++;
}
if (!cards) {
#ifdef MODULE
printk(KERN_ERR CRD_NAME " soundcard not found or device busy\n");
#endif
platform_driver_unregister(&snd_adlib_driver);
return -ENODEV;
}
return 0;
}
static void __exit alsa_card_adlib_exit(void)
{
int i;
for (i = 0; i < SNDRV_CARDS; i++)
platform_device_unregister(devices[i]);
platform_driver_unregister(&snd_adlib_driver);
}
module_init(alsa_card_adlib_init);
module_exit(alsa_card_adlib_exit);
Computing file changes ...
