netdev - [PATCH net-next v5 2/5] bitops: add non-atomic bitops for pointers

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Message-Id: <20210701002759.381983-3-memxor@gmail.com>
Date:   Thu,  1 Jul 2021 05:57:56 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     netdev@...r.kernel.org
Cc:     Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>, bpf@...r.kernel.org
Subject: [PATCH net-next v5 2/5] bitops: add non-atomic bitops for pointers

cpumap needs to set, clear, and test the lowest bit in skb pointer in
various places. To make these checks less noisy, add pointer friendly
bitop macros that also do some typechecking to sanitize the argument.

These wrap the non-atomic bitops __set_bit, __clear_bit, and test_bit
but for pointer arguments. Pointer's address has to be passed in and it
is treated as an unsigned long *, since width and representation of
pointer and unsigned long match on targets Linux supports. They are
prefixed with double underscore to indicate lack of atomicity.

Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
---
 include/linux/bitops.h    | 50 +++++++++++++++++++++++++++++++++++++++
 include/linux/typecheck.h |  9 +++++++
 2 files changed, 59 insertions(+)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 26bf15e6cd35..5e62e2383b7f 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -4,6 +4,7 @@
 
 #include <asm/types.h>
 #include <linux/bits.h>
+#include <linux/typecheck.h>
 
 #include <uapi/linux/kernel.h>
 
@@ -253,6 +254,55 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
 		__clear_bit(nr, addr);
 }
 
+/**
+ * __ptr_set_bit - Set bit in a pointer's value
+ * @nr: the bit to set
+ * @addr: the address of the pointer variable
+ *
+ * Example:
+ *	void *p = foo();
+ *	__ptr_set_bit(bit, &p);
+ */
+#define __ptr_set_bit(nr, addr)                         \
+	({                                              \
+		typecheck_pointer(*(addr));             \
+		__set_bit(nr, (unsigned long *)(addr)); \
+	})
+
+/**
+ * __ptr_clear_bit - Clear bit in a pointer's value
+ * @nr: the bit to clear
+ * @addr: the address of the pointer variable
+ *
+ * Example:
+ *	void *p = foo();
+ *	__ptr_clear_bit(bit, &p);
+ */
+#define __ptr_clear_bit(nr, addr)                         \
+	({                                                \
+		typecheck_pointer(*(addr));               \
+		__clear_bit(nr, (unsigned long *)(addr)); \
+	})
+
+/**
+ * __ptr_test_bit - Test bit in a pointer's value
+ * @nr: the bit to test
+ * @addr: the address of the pointer variable
+ *
+ * Example:
+ *	void *p = foo();
+ *	if (__ptr_test_bit(bit, &p)) {
+ *	        ...
+ *	} else {
+ *		...
+ *	}
+ */
+#define __ptr_test_bit(nr, addr)                       \
+	({                                             \
+		typecheck_pointer(*(addr));            \
+		test_bit(nr, (unsigned long *)(addr)); \
+	})
+
 #ifdef __KERNEL__
 
 #ifndef set_mask_bits
diff --git a/include/linux/typecheck.h b/include/linux/typecheck.h
index 20d310331eb5..46b15e2aaefb 100644
--- a/include/linux/typecheck.h
+++ b/include/linux/typecheck.h
@@ -22,4 +22,13 @@
 	(void)__tmp; \
 })
 
+/*
+ * Check at compile time that something is a pointer type.
+ */
+#define typecheck_pointer(x) \
+({	typeof(x) __dummy; \
+	(void)sizeof(*__dummy); \
+	1; \
+})
+
 #endif		/* TYPECHECK_H_INCLUDED */
-- 
2.31.1