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    Subject[PATCH] futex: cmpxchg_futex_value_locked API change
    Aplogies for the long CC list - as this proposal involves asm changes
    in many architectures, and I have only been able to test on x86,
    I have tried to include one maintainer from every arch so they can
    hopefully double check me. I do think I got all architectures right,
    but you can never be 100% sure...

    ------------------------------------8<---------------------------------

    The cmpxchg_futex_value_locked API was funny in that it returned either
    the original, user-exposed futex value OR an error code such as -EFAULT.
    This was confusing at best, and could be a source of livelocks in places
    that retry the cmpxchg_futex_value_locked after trying to fix the issue
    by running fault_in_user_writeable().

    This change makes the cmpxchg_futex_value_locked API more similar to the
    get_futex_value_locked one, returning an error code and updating the
    original value through a reference argument.

    Signed-off-by: Michel Lespinasse <walken@google.com>
    ---
    arch/alpha/include/asm/futex.h | 22 +++++++++-------
    arch/arm/include/asm/futex.h | 23 +++++++++--------
    arch/frv/include/asm/futex.h | 3 +-
    arch/ia64/include/asm/futex.h | 9 ++++--
    arch/microblaze/include/asm/futex.h | 24 ++++++++++--------
    arch/mips/include/asm/futex.h | 32 +++++++++++++-----------
    arch/parisc/include/asm/futex.h | 18 +++++++-------
    arch/powerpc/include/asm/futex.h | 20 ++++++++-------
    arch/s390/include/asm/futex.h | 4 +-
    arch/s390/include/asm/uaccess.h | 2 +-
    arch/s390/lib/uaccess.h | 4 +-
    arch/s390/lib/uaccess_pt.c | 13 ++++++----
    arch/s390/lib/uaccess_std.c | 6 +++-
    arch/sh/include/asm/futex-irq.h | 9 +++----
    arch/sh/include/asm/futex.h | 5 ++-
    arch/sparc/include/asm/futex_64.h | 16 +++++++----
    arch/tile/include/asm/futex.h | 7 +++--
    arch/x86/include/asm/futex.h | 16 +++++++-----
    include/asm-generic/futex.h | 3 +-
    kernel/futex.c | 46 ++++++++++++----------------------
    20 files changed, 147 insertions(+), 135 deletions(-)

    diff --git a/arch/alpha/include/asm/futex.h b/arch/alpha/include/asm/futex.h
    index 945de22..c4e5c28 100644
    --- a/arch/alpha/include/asm/futex.h
    +++ b/arch/alpha/include/asm/futex.h
    @@ -81,21 +81,22 @@ static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    - int prev, cmp;
    + int ret = 0, prev, cmp;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    __asm__ __volatile__ (
    __ASM_SMP_MB
    - "1: ldl_l %0,0(%2)\n"
    - " cmpeq %0,%3,%1\n"
    - " beq %1,3f\n"
    - " mov %4,%1\n"
    - "2: stl_c %1,0(%2)\n"
    - " beq %1,4f\n"
    + "1: ldl_l %1,0(%3)\n"
    + " cmpeq %1,%4,%2\n"
    + " beq %2,3f\n"
    + " mov %5,%2\n"
    + "2: stl_c %2,0(%3)\n"
    + " beq %2,4f\n"
    "3: .subsection 2\n"
    "4: br 1b\n"
    " .previous\n"
    @@ -105,11 +106,12 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    " .long 2b-.\n"
    " lda $31,3b-2b(%0)\n"
    " .previous\n"
    - : "=&r"(prev), "=&r"(cmp)
    + : "+r"(ret), "=&r"(prev), "=&r"(cmp)
    : "r"(uaddr), "r"((long)oldval), "r"(newval)
    : "memory");

    - return prev;
    + *uval = prev;
    + return ret;
    }

    #endif /* __KERNEL__ */
    diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
    index b33fe70..d20b78f 100644
    --- a/arch/arm/include/asm/futex.h
    +++ b/arch/arm/include/asm/futex.h
    @@ -88,36 +88,37 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    - int val;
    + int ret = 0, val;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    - pagefault_disable(); /* implies preempt_disable() */
    + /* Note that preemption is disabled by futex_atomic_cmpxchg_inatomic
    + * call sites. */

    __asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
    - "1: " T(ldr) " %0, [%3]\n"
    - " teq %0, %1\n"
    + "1: " T(ldr) " %1, [%4]\n"
    + " teq %1, %2\n"
    " it eq @ explicit IT needed for the 2b label\n"
    - "2: " T(streq) " %2, [%3]\n"
    + "2: " T(streq) " %3, [%4]\n"
    "3:\n"
    " .pushsection __ex_table,\"a\"\n"
    " .align 3\n"
    " .long 1b, 4f, 2b, 4f\n"
    " .popsection\n"
    " .pushsection .fixup,\"ax\"\n"
    - "4: mov %0, %4\n"
    + "4: mov %0, %5\n"
    " b 3b\n"
    " .popsection"
    - : "=&r" (val)
    + : "+r" (ret), "=&r" (val)
    : "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
    : "cc", "memory");

    - pagefault_enable(); /* subsumes preempt_enable() */
    -
    - return val;
    + *uval = val;
    + return ret;
    }

    #endif /* !SMP */
    diff --git a/arch/frv/include/asm/futex.h b/arch/frv/include/asm/futex.h
    index 08b3d1d..0548f8e 100644
    --- a/arch/frv/include/asm/futex.h
    +++ b/arch/frv/include/asm/futex.h
    @@ -10,7 +10,8 @@
    extern int futex_atomic_op_inuser(int encoded_op, int __user *uaddr);

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    return -ENOSYS;
    }
    diff --git a/arch/ia64/include/asm/futex.h b/arch/ia64/include/asm/futex.h
    index c7f0f06..b072840 100644
    --- a/arch/ia64/include/asm/futex.h
    +++ b/arch/ia64/include/asm/futex.h
    @@ -100,23 +100,26 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    {
    - register unsigned long r8 __asm ("r8");
    + register unsigned long r8 __asm ("r8") = 0;
    + unsigned long prev;
    __asm__ __volatile__(
    " mf;; \n"
    " mov ar.ccv=%3;; \n"
    "[1:] cmpxchg4.acq %0=[%1],%2,ar.ccv \n"
    " .xdata4 \"__ex_table\", 1b-., 2f-. \n"
    "[2:]"
    - : "=r" (r8)
    + : "=r" (prev)
    : "r" (uaddr), "r" (newval),
    "rO" ((long) (unsigned) oldval)
    : "memory");
    + *uval = prev;
    return r8;
    }
    }
    diff --git a/arch/microblaze/include/asm/futex.h b/arch/microblaze/include/asm/futex.h
    index ad3fd61..fa019ed 100644
    --- a/arch/microblaze/include/asm/futex.h
    +++ b/arch/microblaze/include/asm/futex.h
    @@ -94,31 +94,33 @@ futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    - int prev, cmp;
    + int ret = 0, prev, cmp;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    - __asm__ __volatile__ ("1: lwx %0, %2, r0; \
    - cmp %1, %0, %3; \
    - beqi %1, 3f; \
    - 2: swx %4, %2, r0; \
    - addic %1, r0, 0; \
    - bnei %1, 1b; \
    + __asm__ __volatile__ ("1: lwx %1, %3, r0; \
    + cmp %2, %1, %4; \
    + beqi %2, 3f; \
    + 2: swx %5, %3, r0; \
    + addic %2, r0, 0; \
    + bnei %2, 1b; \
    3: \
    .section .fixup,\"ax\"; \
    4: brid 3b; \
    - addik %0, r0, %5; \
    + addik %0, r0, %6; \
    .previous; \
    .section __ex_table,\"a\"; \
    .word 1b,4b,2b,4b; \
    .previous;" \
    - : "=&r" (prev), "=&r"(cmp) \
    + : "+r" (ret), "=&r" (prev), "=&r"(cmp) \
    : "r" (uaddr), "r" (oldval), "r" (newval), "i" (-EFAULT));

    - return prev;
    + *uval = prev;
    + return ret;
    }

    #endif /* __KERNEL__ */
    diff --git a/arch/mips/include/asm/futex.h b/arch/mips/include/asm/futex.h
    index b9cce90..692a24b 100644
    --- a/arch/mips/include/asm/futex.h
    +++ b/arch/mips/include/asm/futex.h
    @@ -132,9 +132,10 @@ futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    - int retval;
    + int ret = 0, val;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;
    @@ -145,25 +146,25 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    " .set push \n"
    " .set noat \n"
    " .set mips3 \n"
    - "1: ll %0, %2 \n"
    - " bne %0, %z3, 3f \n"
    + "1: ll %1, %3 \n"
    + " bne %1, %z4, 3f \n"
    " .set mips0 \n"
    - " move $1, %z4 \n"
    + " move $1, %z5 \n"
    " .set mips3 \n"
    - "2: sc $1, %1 \n"
    + "2: sc $1, %2 \n"
    " beqzl $1, 1b \n"
    __WEAK_LLSC_MB
    "3: \n"
    " .set pop \n"
    " .section .fixup,\"ax\" \n"
    - "4: li %0, %5 \n"
    + "4: li %0, %6 \n"
    " j 3b \n"
    " .previous \n"
    " .section __ex_table,\"a\" \n"
    " "__UA_ADDR "\t1b, 4b \n"
    " "__UA_ADDR "\t2b, 4b \n"
    " .previous \n"
    - : "=&r" (retval), "=R" (*uaddr)
    + : "+r" (ret), "=&r" (val), "=R" (*uaddr)
    : "R" (*uaddr), "Jr" (oldval), "Jr" (newval), "i" (-EFAULT)
    : "memory");
    } else if (cpu_has_llsc) {
    @@ -172,31 +173,32 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    " .set push \n"
    " .set noat \n"
    " .set mips3 \n"
    - "1: ll %0, %2 \n"
    - " bne %0, %z3, 3f \n"
    + "1: ll %1, %3 \n"
    + " bne %1, %z4, 3f \n"
    " .set mips0 \n"
    - " move $1, %z4 \n"
    + " move $1, %z5 \n"
    " .set mips3 \n"
    - "2: sc $1, %1 \n"
    + "2: sc $1, %2 \n"
    " beqz $1, 1b \n"
    __WEAK_LLSC_MB
    "3: \n"
    " .set pop \n"
    " .section .fixup,\"ax\" \n"
    - "4: li %0, %5 \n"
    + "4: li %0, %6 \n"
    " j 3b \n"
    " .previous \n"
    " .section __ex_table,\"a\" \n"
    " "__UA_ADDR "\t1b, 4b \n"
    " "__UA_ADDR "\t2b, 4b \n"
    " .previous \n"
    - : "=&r" (retval), "=R" (*uaddr)
    + : "+r" (ret), "=&r" (val), "=R" (*uaddr)
    : "R" (*uaddr), "Jr" (oldval), "Jr" (newval), "i" (-EFAULT)
    : "memory");
    } else
    return -ENOSYS;

    - return retval;
    + *uval = val;
    + return ret;
    }

    #endif
    diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
    index 0c705c3..4c6d867 100644
    --- a/arch/parisc/include/asm/futex.h
    +++ b/arch/parisc/include/asm/futex.h
    @@ -51,10 +51,10 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)

    /* Non-atomic version */
    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    - int err = 0;
    - int uval;
    + int val;

    /* futex.c wants to do a cmpxchg_inatomic on kernel NULL, which is
    * our gateway page, and causes no end of trouble...
    @@ -65,12 +65,12 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    - err = get_user(uval, uaddr);
    - if (err) return -EFAULT;
    - if (uval == oldval)
    - err = put_user(newval, uaddr);
    - if (err) return -EFAULT;
    - return uval;
    + if (get_user(val, uaddr))
    + return -EFAULT;
    + if (val == oldval && put_user(newval, uaddr))
    + return -EFAULT;
    + *uval = val;
    + return 0;
    }

    #endif /*__KERNEL__*/
    diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
    index 7c589ef..631e8da 100644
    --- a/arch/powerpc/include/asm/futex.h
    +++ b/arch/powerpc/include/asm/futex.h
    @@ -82,35 +82,37 @@ static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    - int prev;
    + int ret = 0, prev;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    __asm__ __volatile__ (
    PPC_RELEASE_BARRIER
    -"1: lwarx %0,0,%2 # futex_atomic_cmpxchg_inatomic\n\
    - cmpw 0,%0,%3\n\
    +"1: lwarx %1,0,%3 # futex_atomic_cmpxchg_inatomic\n\
    + cmpw 0,%1,%4\n\
    bne- 3f\n"
    - PPC405_ERR77(0,%2)
    -"2: stwcx. %4,0,%2\n\
    + PPC405_ERR77(0,%3)
    +"2: stwcx. %5,0,%3\n\
    bne- 1b\n"
    PPC_ACQUIRE_BARRIER
    "3: .section .fixup,\"ax\"\n\
    -4: li %0,%5\n\
    +4: li %0,%6\n\
    b 3b\n\
    .previous\n\
    .section __ex_table,\"a\"\n\
    .align 3\n\
    " PPC_LONG "1b,4b,2b,4b\n\
    .previous" \
    - : "=&r" (prev), "+m" (*uaddr)
    + : "+r" (ret), "=&r" (prev), "+m" (*uaddr)
    : "r" (uaddr), "r" (oldval), "r" (newval), "i" (-EFAULT)
    : "cc", "memory");

    - return prev;
    + *uval = prev;
    + return ret;
    }

    #endif /* __KERNEL__ */
    diff --git a/arch/s390/include/asm/futex.h b/arch/s390/include/asm/futex.h
    index 5c5d02d..27ac515 100644
    --- a/arch/s390/include/asm/futex.h
    +++ b/arch/s390/include/asm/futex.h
    @@ -39,13 +39,13 @@ static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
    return ret;
    }

    -static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr,
    +static inline int futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    int oldval, int newval)
    {
    if (! access_ok (VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    - return uaccess.futex_atomic_cmpxchg(uaddr, oldval, newval);
    + return uaccess.futex_atomic_cmpxchg(uval, uaddr, oldval, newval);
    }

    #endif /* __KERNEL__ */
    diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
    index d6b1ed0..549adf6 100644
    --- a/arch/s390/include/asm/uaccess.h
    +++ b/arch/s390/include/asm/uaccess.h
    @@ -84,7 +84,7 @@ struct uaccess_ops {
    size_t (*strnlen_user)(size_t, const char __user *);
    size_t (*strncpy_from_user)(size_t, const char __user *, char *);
    int (*futex_atomic_op)(int op, int __user *, int oparg, int *old);
    - int (*futex_atomic_cmpxchg)(int __user *, int old, int new);
    + int (*futex_atomic_cmpxchg)(int *, int __user *, int old, int new);
    };

    extern struct uaccess_ops uaccess;
    diff --git a/arch/s390/lib/uaccess.h b/arch/s390/lib/uaccess.h
    index 126011d..89a8067 100644
    --- a/arch/s390/lib/uaccess.h
    +++ b/arch/s390/lib/uaccess.h
    @@ -12,12 +12,12 @@ extern size_t copy_from_user_std(size_t, const void __user *, void *);
    extern size_t copy_to_user_std(size_t, void __user *, const void *);
    extern size_t strnlen_user_std(size_t, const char __user *);
    extern size_t strncpy_from_user_std(size_t, const char __user *, char *);
    -extern int futex_atomic_cmpxchg_std(int __user *, int, int);
    +extern int futex_atomic_cmpxchg_std(int *, int __user *, int, int);
    extern int futex_atomic_op_std(int, int __user *, int, int *);

    extern size_t copy_from_user_pt(size_t, const void __user *, void *);
    extern size_t copy_to_user_pt(size_t, void __user *, const void *);
    extern int futex_atomic_op_pt(int, int __user *, int, int *);
    -extern int futex_atomic_cmpxchg_pt(int __user *, int, int);
    +extern int futex_atomic_cmpxchg_pt(int *, int __user *, int, int);

    #endif /* __ARCH_S390_LIB_UACCESS_H */
    diff --git a/arch/s390/lib/uaccess_pt.c b/arch/s390/lib/uaccess_pt.c
    index 404f2de..e4f9ad8 100644
    --- a/arch/s390/lib/uaccess_pt.c
    +++ b/arch/s390/lib/uaccess_pt.c
    @@ -354,26 +354,29 @@ int futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
    return ret;
    }

    -static int __futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
    +static int __futex_atomic_cmpxchg_pt(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    int ret;

    asm volatile("0: cs %1,%4,0(%5)\n"
    - "1: lr %0,%1\n"
    + "1: l %0,0\n"
    "2:\n"
    EX_TABLE(0b,2b) EX_TABLE(1b,2b)
    : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
    : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
    : "cc", "memory" );
    + *uval = oldval;
    return ret;
    }

    -int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
    +int futex_atomic_cmpxchg_pt(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    int ret;

    if (segment_eq(get_fs(), KERNEL_DS))
    - return __futex_atomic_cmpxchg_pt(uaddr, oldval, newval);
    + return __futex_atomic_cmpxchg_pt(uval, uaddr, oldval, newval);
    spin_lock(&current->mm->page_table_lock);
    uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
    if (!uaddr) {
    @@ -382,7 +385,7 @@ int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
    }
    get_page(virt_to_page(uaddr));
    spin_unlock(&current->mm->page_table_lock);
    - ret = __futex_atomic_cmpxchg_pt(uaddr, oldval, newval);
    + ret = __futex_atomic_cmpxchg_pt(uval, uaddr, oldval, newval);
    put_page(virt_to_page(uaddr));
    return ret;
    }
    diff --git a/arch/s390/lib/uaccess_std.c b/arch/s390/lib/uaccess_std.c
    index a6c4f7e..5c568b3 100644
    --- a/arch/s390/lib/uaccess_std.c
    +++ b/arch/s390/lib/uaccess_std.c
    @@ -287,19 +287,21 @@ int futex_atomic_op_std(int op, int __user *uaddr, int oparg, int *old)
    return ret;
    }

    -int futex_atomic_cmpxchg_std(int __user *uaddr, int oldval, int newval)
    +int futex_atomic_cmpxchg_std(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    int ret;

    asm volatile(
    " sacf 256\n"
    "0: cs %1,%4,0(%5)\n"
    - "1: lr %0,%1\n"
    + "1: l %0,0\n"
    "2: sacf 0\n"
    EX_TABLE(0b,2b) EX_TABLE(1b,2b)
    : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
    : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
    : "cc", "memory" );
    + *uval = oldval;
    return ret;
    }

    diff --git a/arch/sh/include/asm/futex-irq.h b/arch/sh/include/asm/futex-irq.h
    index a9f16a7..7b701cb 100644
    --- a/arch/sh/include/asm/futex-irq.h
    +++ b/arch/sh/include/asm/futex-irq.h
    @@ -88,7 +88,8 @@ static inline int atomic_futex_op_xchg_xor(int oparg, int __user *uaddr,
    return ret;
    }

    -static inline int atomic_futex_op_cmpxchg_inatomic(int __user *uaddr,
    +static inline int atomic_futex_op_cmpxchg_inatomic(int *uval,
    + int __user *uaddr,
    int oldval, int newval)
    {
    unsigned long flags;
    @@ -102,10 +103,8 @@ static inline int atomic_futex_op_cmpxchg_inatomic(int __user *uaddr,

    local_irq_restore(flags);

    - if (ret)
    - return ret;
    -
    - return prev;
    + *uval = prev;
    + return ret;
    }

    #endif /* __ASM_SH_FUTEX_IRQ_H */
    diff --git a/arch/sh/include/asm/futex.h b/arch/sh/include/asm/futex.h
    index 68256ec..a8a5125 100644
    --- a/arch/sh/include/asm/futex.h
    +++ b/arch/sh/include/asm/futex.h
    @@ -65,12 +65,13 @@ static inline int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    - return atomic_futex_op_cmpxchg_inatomic(uaddr, oldval, newval);
    + return atomic_futex_op_cmpxchg_inatomic(uval, uaddr, oldval, newval);
    }

    #endif /* __KERNEL__ */
    diff --git a/arch/sparc/include/asm/futex_64.h b/arch/sparc/include/asm/futex_64.h
    index 47f9583..e086220 100644
    --- a/arch/sparc/include/asm/futex_64.h
    +++ b/arch/sparc/include/asm/futex_64.h
    @@ -85,26 +85,30 @@ static inline int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    + int ret = 0;
    +
    __asm__ __volatile__(
    - "\n1: casa [%3] %%asi, %2, %0\n"
    + "\n1: casa [%4] %%asi, %3, %1\n"
    "2:\n"
    " .section .fixup,#alloc,#execinstr\n"
    " .align 4\n"
    "3: sethi %%hi(2b), %0\n"
    " jmpl %0 + %%lo(2b), %%g0\n"
    - " mov %4, %0\n"
    + " mov %5, %0\n"
    " .previous\n"
    " .section __ex_table,\"a\"\n"
    " .align 4\n"
    " .word 1b, 3b\n"
    " .previous\n"
    - : "=r" (newval)
    - : "0" (newval), "r" (oldval), "r" (uaddr), "i" (-EFAULT)
    + : "+r" (ret), "=r" (newval)
    + : "1" (newval), "r" (oldval), "r" (uaddr), "i" (-EFAULT)
    : "memory");

    - return newval;
    + *uval = newval;
    + return ret;
    }

    #endif /* !(_SPARC64_FUTEX_H) */
    diff --git a/arch/tile/include/asm/futex.h b/arch/tile/include/asm/futex.h
    index fe0d10d..664b20a 100644
    --- a/arch/tile/include/asm/futex.h
    +++ b/arch/tile/include/asm/futex.h
    @@ -119,8 +119,8 @@ static inline int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
    return ret;
    }

    -static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval,
    - int newval)
    +static inline int futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    struct __get_user asm_ret;

    @@ -128,7 +128,8 @@ static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval,
    return -EFAULT;

    asm_ret = futex_cmpxchg(uaddr, oldval, newval);
    - return asm_ret.err ? asm_ret.err : asm_ret.val;
    + *uval = asm_ret.val;
    + return asm_ret.err;
    }

    #ifndef __tilegx__
    diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
    index 1f11ce4..884c0b5 100644
    --- a/arch/x86/include/asm/futex.h
    +++ b/arch/x86/include/asm/futex.h
    @@ -109,9 +109,10 @@ static inline int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
    return ret;
    }

    -static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval,
    - int newval)
    +static inline int futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    + int ret = 0;

    #if defined(CONFIG_X86_32) && !defined(CONFIG_X86_BSWAP)
    /* Real i386 machines have no cmpxchg instruction */
    @@ -122,18 +123,19 @@ static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval,
    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
    return -EFAULT;

    - asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %3, %1\n"
    + asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %4, %2\n"
    "2:\t.section .fixup, \"ax\"\n"
    - "3:\tmov %2, %0\n"
    + "3:\tmov %3, %0\n"
    "\tjmp 2b\n"
    "\t.previous\n"
    _ASM_EXTABLE(1b, 3b)
    - : "=a" (oldval), "+m" (*uaddr)
    - : "i" (-EFAULT), "r" (newval), "0" (oldval)
    + : "+r" (ret), "=a" (oldval), "+m" (*uaddr)
    + : "i" (-EFAULT), "r" (newval), "1" (oldval)
    : "memory"
    );

    - return oldval;
    + *uval = oldval;
    + return ret;
    }

    #endif
    diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
    index 3c2344f..132bf52 100644
    --- a/include/asm-generic/futex.h
    +++ b/include/asm-generic/futex.h
    @@ -48,7 +48,8 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
    }

    static inline int
    -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
    +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
    + int oldval, int newval)
    {
    return -ENOSYS;
    }
    diff --git a/kernel/futex.c b/kernel/futex.c
    index 3184d3b..53b783f 100644
    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -381,15 +381,16 @@ static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
    return NULL;
    }

    -static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
    +static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
    + u32 uval, u32 newval)
    {
    - u32 curval;
    + int ret;

    pagefault_disable();
    - curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
    + ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
    pagefault_enable();

    - return curval;
    + return ret;
    }

    static int get_futex_value_locked(u32 *dest, u32 __user *from)
    @@ -688,9 +689,7 @@ retry:
    if (set_waiters)
    newval |= FUTEX_WAITERS;

    - curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
    -
    - if (unlikely(curval == -EFAULT))
    + if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
    return -EFAULT;

    /*
    @@ -728,9 +727,7 @@ retry:
    lock_taken = 1;
    }

    - curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
    -
    - if (unlikely(curval == -EFAULT))
    + if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
    return -EFAULT;
    if (unlikely(curval != uval))
    goto retry;
    @@ -843,9 +840,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)

    newval = FUTEX_WAITERS | task_pid_vnr(new_owner);

    - curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
    -
    - if (curval == -EFAULT)
    + if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
    ret = -EFAULT;
    else if (curval != uval)
    ret = -EINVAL;
    @@ -880,10 +875,8 @@ static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
    * There is no waiter, so we unlock the futex. The owner died
    * bit has not to be preserved here. We are the owner:
    */
    - oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
    -
    - if (oldval == -EFAULT)
    - return oldval;
    + if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
    + return -EFAULT;
    if (oldval != uval)
    return -EAGAIN;

    @@ -1578,9 +1571,7 @@ retry:
    while (1) {
    newval = (uval & FUTEX_OWNER_DIED) | newtid;

    - curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
    -
    - if (curval == -EFAULT)
    + if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
    goto handle_fault;
    if (curval == uval)
    break;
    @@ -2073,11 +2064,9 @@ retry:
    * again. If it succeeds then we can return without waking
    * anyone else up:
    */
    - if (!(uval & FUTEX_OWNER_DIED))
    - uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
    -
    -
    - if (unlikely(uval == -EFAULT))
    + if (!(uval & FUTEX_OWNER_DIED) &&
    + unlikely(cmpxchg_futex_value_locked(&uval, uaddr,
    + task_pid_vnr(current), 0)))
    goto pi_faulted;
    /*
    * Rare case: we managed to release the lock atomically,
    @@ -2464,9 +2453,7 @@ retry:
    * userspace.
    */
    mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
    - nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
    -
    - if (nval == -EFAULT)
    + if (futex_atomic_cmpxchg_inatomic(&nval, uaddr, uval, mval))
    return -1;

    if (nval != uval)
    @@ -2679,8 +2666,7 @@ static int __init futex_init(void)
    * implementation, the non-functional ones will return
    * -ENOSYS.
    */
    - curval = cmpxchg_futex_value_locked(NULL, 0, 0);
    - if (curval == -EFAULT)
    + if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
    futex_cmpxchg_enabled = 1;

    for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
    --
    1.7.3.1


    --
    Michel "Walken" Lespinasse
    A program is never fully debugged until the last user dies.


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