ptrace: remove PTRACE_SEIZE_DEVEL bit

PTRACE_SEIZE code is tested and ready for production use, remove the
code which requires special bit in data argument to make PTRACE_SEIZE
work.

Strace team prepares for a new release of strace, and we would like to
ship the code which uses PTRACE_SEIZE, preferably after this change goes
into released kernel.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/ptrace.h

@@ -51,9 +51,6 @@
 #define PTRACE_INTERRUPT	0x4207
 #define PTRACE_LISTEN		0x4208
 
-/* flags in @data for PTRACE_SEIZE */
-#define PTRACE_SEIZE_DEVEL	0x80000000 /* temp flag for development */
-
 /* Wait extended result codes for the above trace options.  */
 #define PTRACE_EVENT_FORK	1
 #define PTRACE_EVENT_VFORK	2
@@ -64,7 +61,7 @@
 /* Extended result codes which enabled by means other than options.  */
 #define PTRACE_EVENT_STOP	128
 
-/* options set using PTRACE_SETOPTIONS */
+/* Options set using PTRACE_SETOPTIONS or using PTRACE_SEIZE @data param */
 #define PTRACE_O_TRACESYSGOOD	1
 #define PTRACE_O_TRACEFORK	(1 << PTRACE_EVENT_FORK)
 #define PTRACE_O_TRACEVFORK	(1 << PTRACE_EVENT_VFORK)

kernel/ptrace.c

@@ -237,25 +237,10 @@ static int ptrace_attach(struct task_struct *task, long request,
 	bool seize = (request == PTRACE_SEIZE);
 	int retval;
 
-	/*
-	 * SEIZE will enable new ptrace behaviors which will be implemented
-	 * gradually.  SEIZE_DEVEL bit is used to prevent applications
-	 * expecting full SEIZE behaviors trapping on kernel commits which
-	 * are still in the process of implementing them.
-	 *
-	 * Only test programs for new ptrace behaviors being implemented
-	 * should set SEIZE_DEVEL.  If unset, SEIZE will fail with -EIO.
-	 *
-	 * Once SEIZE behaviors are completely implemented, this flag
-	 * will be removed.
-	 */
 	retval = -EIO;
 	if (seize) {
 		if (addr != 0)
 			goto out;
-		if (!(flags & PTRACE_SEIZE_DEVEL))
-			goto out;
-		flags &= ~(unsigned long)PTRACE_SEIZE_DEVEL;
 		if (flags & ~(unsigned long)PTRACE_O_MASK)
 			goto out;
 		flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT);