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SubjectRe: Kernel crash after using new Intel NIC (igb)
On Fri, May 27, 2011 at 09:56:59PM +0200, Eric Dumazet wrote:
> >
> > This looks very similar to atomic_add_unless(). If we had a
> >
> > __atomic_add_unless() that returned "old", we could then do:
> >
> > atomic_add_unless() { return __atomic_add_unless() != u }
> > atomic_add_unless_return() { return __atomic_add_unless() + a}
> >
>
> Sure !
>
> I preferred to not touch lot of files in kernel (atomic_add_unless() is
> defined in several files) because its a stable candidate patch (2.6.36+)
>
> So a cleanup patch for 2.6.40+ is certainly doable, do you want to do
> this ?

The attached works for me for x86_64. Cc'ing Ingo/Thomas for comment.

-Arun

atomic: Refactor atomic_add_unless

Commit 686a7e3 (inetpeer: fix race in unused_list manipulations)
in net-2.6 added a atomic_add_unless_return() variant that tries
to detect 0->1 transitions of an atomic reference count.

This sounds like a generic functionality that could be expressed
in terms of an __atomic_add_unless() that returned the old value
instead of a bool.

Signed-off-by: Arun Sharma <asharma@fb.com>
---
arch/x86/include/asm/atomic.h | 22 ++++++++++++++++++----
1 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
index 952a826..bbdbffe 100644
--- a/arch/x86/include/asm/atomic.h
+++ b/arch/x86/include/asm/atomic.h
@@ -221,15 +221,15 @@ static inline int atomic_xchg(atomic_t *v, int new)
}

/**
- * atomic_add_unless - add unless the number is already a given value
+ * __atomic_add_unless - add unless the number is already a given value
* @v: pointer of type atomic_t
* @a: the amount to add to v...
* @u: ...unless v is equal to u.
*
* Atomically adds @a to @v, so long as @v was not already @u.
- * Returns non-zero if @v was not @u, and zero otherwise.
+ * Returns the old value of v
*/
-static inline int atomic_add_unless(atomic_t *v, int a, int u)
+static inline int __atomic_add_unless(atomic_t *v, int a, int u)
{
int c, old;
c = atomic_read(v);
@@ -241,7 +241,21 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
break;
c = old;
}
- return c != (u);
+ return c;
+}
+
+/**
+ * atomic_add_unless - add unless the number is already a given value
+ * @v: pointer of type atomic_t
+ * @a: the amount to add to v...
+ * @u: ...unless v is equal to u.
+ *
+ * Atomically adds @a to @v, so long as @v was not already @u.
+ * Returns non-zero if @v was not @u, and zero otherwise.
+ */
+static inline int atomic_add_unless(atomic_t *v, int a, int u)
+{
+ return __atomic_add_unless(v, a, u) != u;
}

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
--
1.7.4


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