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
mmzone.h
/*
* Written by Kanoj Sarcar (kanoj@sgi.com) Aug 99
* Adapted for the alpha wildfire architecture Jan 2001.
*/
#ifndef _ASM_MMZONE_H_
#define _ASM_MMZONE_H_
#include <asm/smp.h>
struct bootmem_data_t; /* stupid forward decl. */
/*
* Following are macros that are specific to this numa platform.
*/
extern pg_data_t node_data[];
#define alpha_pa_to_nid(pa) \
(alpha_mv.pa_to_nid \
? alpha_mv.pa_to_nid(pa) \
: (0))
#define node_mem_start(nid) \
(alpha_mv.node_mem_start \
? alpha_mv.node_mem_start(nid) \
: (0UL))
#define node_mem_size(nid) \
(alpha_mv.node_mem_size \
? alpha_mv.node_mem_size(nid) \
: ((nid) ? (0UL) : (~0UL)))
#define pa_to_nid(pa) alpha_pa_to_nid(pa)
#define NODE_DATA(nid) (&node_data[(nid)])
#define node_localnr(pfn, nid) ((pfn) - NODE_DATA(nid)->node_start_pfn)
#if 1
#define PLAT_NODE_DATA_LOCALNR(p, n) \
(((p) >> PAGE_SHIFT) - PLAT_NODE_DATA(n)->gendata.node_start_pfn)
#else
static inline unsigned long
PLAT_NODE_DATA_LOCALNR(unsigned long p, int n)
{
unsigned long temp;
temp = p >> PAGE_SHIFT;
return temp - PLAT_NODE_DATA(n)->gendata.node_start_pfn;
}
#endif
#ifdef CONFIG_DISCONTIGMEM
/*
* Following are macros that each numa implementation must define.
*/
/*
* Given a kernel address, find the home node of the underlying memory.
*/
#define kvaddr_to_nid(kaddr) pa_to_nid(__pa(kaddr))
#define node_start_pfn(nid) (NODE_DATA(nid)->node_start_pfn)
/*
* Given a kaddr, LOCAL_BASE_ADDR finds the owning node of the memory
* and returns the kaddr corresponding to first physical page in the
* node's mem_map.
*/
#define LOCAL_BASE_ADDR(kaddr) \
((unsigned long)__va(NODE_DATA(kvaddr_to_nid(kaddr))->node_start_pfn \
<< PAGE_SHIFT))
/* XXX: FIXME -- wli */
#define kern_addr_valid(kaddr) (0)
#define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
#define VALID_PAGE(page) (((page) - mem_map) < max_mapnr)
#define pmd_page(pmd) (pfn_to_page(pmd_val(pmd) >> 32))
#define pte_pfn(pte) (pte_val(pte) >> 32)
#define mk_pte(page, pgprot) \
({ \
pte_t pte; \
unsigned long pfn; \
\
pfn = page_to_pfn(page) << 32; \
pte_val(pte) = pfn | pgprot_val(pgprot); \
\
pte; \
})
#define pte_page(x) \
({ \
unsigned long kvirt; \
struct page * __xx; \
\
kvirt = (unsigned long)__va(pte_val(x) >> (32-PAGE_SHIFT)); \
__xx = virt_to_page(kvirt); \
\
__xx; \
})
#define page_to_pa(page) \
(page_to_pfn(page) << PAGE_SHIFT)
#define pfn_to_nid(pfn) pa_to_nid(((u64)(pfn) << PAGE_SHIFT))
#define pfn_valid(pfn) \
(((pfn) - node_start_pfn(pfn_to_nid(pfn))) < \
node_spanned_pages(pfn_to_nid(pfn))) \
#define virt_addr_valid(kaddr) pfn_valid((__pa(kaddr) >> PAGE_SHIFT))
#endif /* CONFIG_DISCONTIGMEM */
#endif /* _ASM_MMZONE_H_ */
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