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Subject[RESEND PATCH] sched: fix build with GCC_PLUGIN_RANDSTRUCT
Date
From: Mike Rapoport <rppt@linux.ibm.com>

Since the commit a148866489fb ("sched: Replace rq::wake_list")
task_struct and CSD_TYPE_TTWU objects can be on the same queue and this
requires that have "layout similar enough".

This assumption is broken when CONFIG_GCC_PLUGIN_RANDSTRUCT is enabled:

CHK include/generated/compile.h
CC kernel/smp.o
In file included from arch/x86/include/asm/atomic.h:5,
from include/linux/atomic.h:7,
from include/linux/llist.h:51,
from include/linux/irq_work.h:5,
from kernel/smp.c:10:
kernel/smp.c: In function ‘smp_init’:
include/linux/compiler.h:392:38: error: call to ‘__compiletime_assert_157’ declared with attribute error: BUILD_BUG_ON failed: offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) != offsetof(struct __call_single_data, flags) - offsetof(struct __call_single_data, llist)
392 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^
include/linux/compiler.h:373:4: note: in definition of macro ‘__compiletime_assert’
373 | prefix ## suffix(); \
| ^~~~~~
include/linux/compiler.h:392:2: note: in expansion of macro ‘_compiletime_assert’
392 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^~~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
| ^~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
| ^~~~~~~~~~~~~~~~
kernel/smp.c:687:2: note: in expansion of macro ‘BUILD_BUG_ON’
687 | BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) !=
| ^~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:280: kernel/smp.o] Error 1
make[1]: *** [Makefile:1764: kernel] Error 2
make[1]: *** Waiting for unfinished jobs....
make[1]: Leaving directory '/home/mike/build/kernel'
make: *** [Makefile:185: __sub-make] Error 2

Move 'wake_entry' and 'wake_entry_type' fiels of task_struct out of the
randomized fields to keep their layout intact.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
include/linux/sched.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b62e6aaf28f0..c885573669ac 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -641,6 +641,15 @@ struct task_struct {
/* -1 unrunnable, 0 runnable, >0 stopped: */
volatile long state;

+ /*
+ * The layout of these fields must match the layout CSD_TYPE_TTWU
+ * so they can be on the same @call_single_queue
+ */
+#ifdef CONFIG_SMP
+ struct llist_node wake_entry;
+ unsigned int wake_entry_type;
+#endif
+
/*
* This begins the randomizable portion of task_struct. Only
* scheduling-critical items should be added above here.
@@ -654,8 +663,6 @@ struct task_struct {
unsigned int ptrace;

#ifdef CONFIG_SMP
- struct llist_node wake_entry;
- unsigned int wake_entry_type;
int on_cpu;
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* Current CPU: */
--
2.25.4
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