um: move thread info into task

This selects the THREAD_INFO_IN_TASK option for UM and changes the way
that the current task is discovered. This is trivial though, as UML
already tracks the current task in cpu_tasks[] and this can be used to
retrieve it.

Also remove the signal handler code that copies the thread information
into the IRQ stack. It is obsolete now, which also means that the
mentioned race condition cannot happen anymore.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Reviewed-by: Hajime Tazaki <thehajime@gmail.com>
Link: https://patch.msgid.link/20241111102910.46512-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

4 files changed, 25 insertions, 22 deletions

diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
index 18f902da8e99..428f2c5158c2 100644
--- a/arch/um/include/asm/Kbuild
+++ b/arch/um/include/asm/Kbuild
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 generic-y += bug.h
 generic-y += compat.h
-generic-y += current.h
 generic-y += device.h
 generic-y += dma-mapping.h
 generic-y += emergency-restart.h
diff --git a/arch/um/include/asm/current.h b/arch/um/include/asm/current.h
new file mode 100644
index 000000000000..de64e032d66c
--- /dev/null
+++ b/arch/um/include/asm/current.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_CURRENT_H
+#define __ASM_CURRENT_H
+
+#include <linux/compiler.h>
+#include <linux/threads.h>
+
+#ifndef __ASSEMBLY__
+
+struct task_struct;
+extern struct task_struct *cpu_tasks[NR_CPUS];
+
+static __always_inline struct task_struct *get_current(void)
+{
+	return cpu_tasks[0];
+}
+
+
+#define current get_current()
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_CURRENT_H */
diff --git a/arch/um/include/asm/thread_info.h b/arch/um/include/asm/thread_info.h
index 4d2a768246bc..f9ad06fcc991 100644
--- a/arch/um/include/asm/thread_info.h
+++ b/arch/um/include/asm/thread_info.h
@@ -17,33 +17,17 @@
 #include <sysdep/ptrace_user.h>
 
 struct thread_info {
-	struct task_struct	*task;		/* main task structure */
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
-	struct thread_info	*real_thread;    /* Points to non-IRQ stack */
 };
 
 #define INIT_THREAD_INFO(tsk)			\
 {						\
-	.task =		&tsk,			\
 	.flags =		0,		\
 	.cpu =		0,			\
 	.preempt_count = INIT_PREEMPT_COUNT,	\
-	.real_thread = NULL,			\
-}
-
-/* how to get the thread information struct from C */
-static inline struct thread_info *current_thread_info(void)
-{
-	struct thread_info *ti;
-	unsigned long mask = THREAD_SIZE - 1;
-	void *p;
-
-	asm volatile ("" : "=r" (p) : "0" (&ti));
-	ti = (struct thread_info *) (((unsigned long)p) & ~mask);
-	return ti;
 }
 
 #endif
diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index d9679c911e54..ea65f151bf48 100644
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -30,11 +30,8 @@
 
 #include <sysdep/ptrace.h>
 
-struct cpu_task {
-	void *task;
-};
-
-extern struct cpu_task cpu_tasks[];
+struct task_struct;
+extern struct task_struct *cpu_tasks[];
 
 extern unsigned long long physmem_size;