sched/preempt, futex: Update comments to clarify that preemption doesn't have to...

As arm64 and arc have no special implementations for !CONFIG_SMP, mutual
exclusion doesn't seem to rely on preemption.

Let's make it clear in the comments that preemption doesn't have to be
disabled when accessing user space in the futex code, so we can remove
preempt_disable() from pagefault_disable().

Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-13-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/arc/include/asm/futex.h b/arch/arc/include/asm/futex.h
index 4dc64ddebecebe354ef90b14fe28bc8804569a52..05b5aaf5b0f91e5580395e08ae778f5ddace5b3c 100644 (file)
--- a/arch/arc/include/asm/futex.h
+++ b/arch/arc/include/asm/futex.h
@@ -53,7 +53,7 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
        if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
                return -EFAULT;
 
-       pagefault_disable();    /* implies preempt_disable() */
+       pagefault_disable();
 
        switch (op) {
        case FUTEX_OP_SET:
@@ -75,7 +75,7 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
                ret = -ENOSYS;
        }
 
-       pagefault_enable();     /* subsumes preempt_enable() */
+       pagefault_enable();
 
        if (!ret) {
                switch (cmp) {
@@ -104,7 +104,7 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
        return ret;
 }
 
-/* Compare-xchg with preemption disabled.
+/* Compare-xchg with pagefaults disabled.
  *  Notes:
  *      -Best-Effort: Exchg happens only if compare succeeds.
  *          If compare fails, returns; leaving retry/looping to upper layers
@@ -121,7 +121,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 oldval,
        if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
                return -EFAULT;
 
-       pagefault_disable();    /* implies preempt_disable() */
+       pagefault_disable();
 
        /* TBD : can use llock/scond */
        __asm__ __volatile__(
@@ -142,7 +142,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 oldval,
        : "r"(oldval), "r"(newval), "r"(uaddr), "ir"(-EFAULT)
        : "cc", "memory");
 
-       pagefault_enable();     /* subsumes preempt_enable() */
+       pagefault_enable();
 
        *uval = val;
        return val;

diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 5f750dc96e0fd64123851ac787659f5953bc71e5..74069b3bd919c7ff3c5722f9f2c1dce212abd3fd 100644 (file)
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -58,7 +58,7 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
        if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
                return -EFAULT;
 
-       pagefault_disable();    /* implies preempt_disable() */
+       pagefault_disable();
 
        switch (op) {
        case FUTEX_OP_SET:
@@ -85,7 +85,7 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
                ret = -ENOSYS;
        }
 
-       pagefault_enable();     /* subsumes preempt_enable() */
+       pagefault_enable();
 
        if (!ret) {
                switch (cmp) {