This patch enables tracking semaphore ownership. It saves a pointer to the
thread_info struct of the last process that got a semaphore. I couldn't
think of a better way to print out the info, so I hacked up the code that
dumps a process's kernel stack so it prints out the PID of the owning process
when it finds another process waiting for a semaphore.
So far it has worked under some light testing and should be fairly safe to use.
In general, if a process is sleeping on a semaphore, that semaphore shouldn't
disappear while this code is referencing it and neither should the owner.
Since this is really meant for finding deadlocks and not for general use I
think it should be OK.
Signed-off-by: Chuck Ebbert <[email protected]>
arch/i386/kernel/semaphore.c | 16 ++++++++++
arch/i386/kernel/traps.c | 10 ++++++
include/asm-i386/semaphore.h | 66 ++++++++++++++++++++++++++++++++++++++-----
lib/Kconfig.debug | 9 +++++
4 files changed, 94 insertions(+), 7 deletions(-)
--- 2.6.13-rc6c.orig/include/asm-i386/semaphore.h
+++ 2.6.13-rc6c/include/asm-i386/semaphore.h
@@ -45,15 +45,29 @@ struct semaphore {
atomic_t count;
int sleepers;
wait_queue_head_t wait;
+#ifdef CONFIG_SEMAPHORE_OWNER
+ struct thread_info *owner;
+#endif
};
-
+#ifdef CONFIG_SEMAPHORE_OWNER
+void __down_return(void);
+void __down_intr_return(void);
+#define __SEMAPHORE_INITIALIZER(name, n) \
+{ \
+ .count = ATOMIC_INIT(n), \
+ .sleepers = 0, \
+ .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait), \
+ .owner = NULL, \
+}
+#else
#define __SEMAPHORE_INITIALIZER(name, n) \
{ \
.count = ATOMIC_INIT(n), \
.sleepers = 0, \
.wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
}
+#endif /* CONFIG_SEMAPHORE_OWNER */
#define __MUTEX_INITIALIZER(name) \
__SEMAPHORE_INITIALIZER(name,1)
@@ -75,6 +89,9 @@ static inline void sema_init (struct sem
atomic_set(&sem->count, val);
sem->sleepers = 0;
init_waitqueue_head(&sem->wait);
+#ifdef CONFIG_SEMAPHORE_OWNER
+ sem->owner = NULL;
+#endif
}
static inline void init_MUTEX (struct semaphore *sem)
@@ -105,13 +122,22 @@ static inline void down(struct semaphore
LOCK "decl %0\n\t" /* --sem->count */
"js 2f\n"
"1:\n"
+#ifdef CONFIG_SEMAPHORE_OWNER
+ "andl %%esp,%1\n"
+#endif
LOCK_SECTION_START("")
"2:\tlea %0,%%eax\n\t"
"call __down_failed\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=m" (sem->count)
+#ifdef CONFIG_SEMAPHORE_OWNER
+ , "=r" (sem->owner)
+#endif
:
+#ifdef CONFIG_SEMAPHORE_OWNER
+ "1" (~(THREAD_SIZE - 1))
+#endif
:"memory","ax");
}
@@ -127,16 +153,29 @@ static inline int down_interruptible(str
__asm__ __volatile__(
"# atomic interruptible down operation\n\t"
LOCK "decl %1\n\t" /* --sem->count */
- "js 2f\n\t"
+ "js 3f\n\t"
"xorl %0,%0\n"
"1:\n"
+#ifdef CONFIG_SEMAPHORE_OWNER
+ "or %0,%0\n"
+ "jnz 2f\n"
+ "andl %%esp,%3\n"
+ "movl %3,%2\n"
+ "2:\n"
+#endif
LOCK_SECTION_START("")
- "2:\tlea %1,%%eax\n\t"
+ "3:\tlea %1,%%eax\n\t"
"call __down_failed_interruptible\n\t"
"jmp 1b\n"
LOCK_SECTION_END
- :"=a" (result), "=m" (sem->count)
+ :"=&a" (result), "=m" (sem->count)
+#ifdef CONFIG_SEMAPHORE_OWNER
+ , "=m" (sem->owner)
+#endif
:
+#ifdef CONFIG_SEMAPHORE_OWNER
+ "r" (~(THREAD_SIZE - 1))
+#endif
:"memory");
return result;
}
@@ -152,16 +191,29 @@ static inline int down_trylock(struct se
__asm__ __volatile__(
"# atomic interruptible down operation\n\t"
LOCK "decl %1\n\t" /* --sem->count */
- "js 2f\n\t"
+ "js 3f\n\t"
"xorl %0,%0\n"
"1:\n"
+#ifdef CONFIG_SEMAPHORE_OWNER
+ "or %0,%0\n"
+ "jnz 2f\n"
+ "andl %%esp,%3\n"
+ "movl %3,%2\n"
+ "2:\n"
+#endif
LOCK_SECTION_START("")
- "2:\tlea %1,%%eax\n\t"
+ "3:\tlea %1,%%eax\n\t"
"call __down_failed_trylock\n\t"
"jmp 1b\n"
LOCK_SECTION_END
- :"=a" (result), "=m" (sem->count)
+ :"=&a" (result), "=m" (sem->count)
+#ifdef CONFIG_SEMAPHORE_OWNER
+ , "=m" (sem->owner)
+#endif
:
+#ifdef CONFIG_SEMAPHORE_OWNER
+ "r" (~(THREAD_SIZE - 1))
+#endif
:"memory");
return result;
}
--- 2.6.13-rc6c.orig/arch/i386/kernel/semaphore.c
+++ 2.6.13-rc6c/arch/i386/kernel/semaphore.c
@@ -198,7 +198,15 @@ asm(
#endif
"pushl %edx\n\t"
"pushl %ecx\n\t"
+#if defined(CONFIG_SEMAPHORE_OWNER)
+ "pushl %eax\n\t"
+#endif
"call __down\n\t"
+#if defined(CONFIG_SEMAPHORE_OWNER)
+"\n.globl __down_return\n"
+"__down_return:\n\t"
+ "popl %ecx\n\t"
+#endif
"popl %ecx\n\t"
"popl %edx\n\t"
#if defined(CONFIG_FRAME_POINTER)
@@ -219,7 +227,15 @@ asm(
#endif
"pushl %edx\n\t"
"pushl %ecx\n\t"
+#if defined(CONFIG_SEMAPHORE_OWNER)
+ "pushl %eax\n\t"
+#endif
"call __down_interruptible\n\t"
+#if defined(CONFIG_SEMAPHORE_OWNER)
+"\n.globl __down_intr_return\n"
+"__down_intr_return:\n\t"
+ "popl %ecx\n\t"
+#endif
"popl %ecx\n\t"
"popl %edx\n\t"
#if defined(CONFIG_FRAME_POINTER)
--- 2.6.13-rc6c.orig/lib/Kconfig.debug
+++ 2.6.13-rc6c/lib/Kconfig.debug
@@ -159,3 +159,12 @@ config FRAME_POINTER
If you don't debug the kernel, you can say N, but we may not be able
to solve problems without frame pointers.
+config SEMAPHORE_OWNER
+ bool "Track semaphore owners"
+ depends on DEBUG_KERNEL && FRAME_POINTER && (X86 && !X86_64)
+ default n
+ help
+ Say Y to enable tracking of semaphore owners.
+
+ If unsure, say N.
+
--- 2.6.13-rc6c.orig/arch/i386/kernel/traps.c
+++ 2.6.13-rc6c/arch/i386/kernel/traps.c
@@ -123,6 +123,16 @@ static inline unsigned long print_contex
addr = *(unsigned long *)(ebp + 4);
printk(" [<%08lx>] ", addr);
print_symbol("%s", addr);
+#ifdef CONFIG_SEMAPHORE_OWNER
+ if (addr == (unsigned long)__down_return
+ || addr == (unsigned long)__down_intr_return) {
+ struct semaphore *sem = *(struct semaphore **)(ebp + 8);
+ if (sem && !((unsigned long)sem->owner & (THREAD_SIZE - 1)))
+ printk(" sem owner %s %d",
+ sem->owner ? "pid" : "(none)",
+ sem->owner ? sem->owner->task->pid : 0);
+ }
+#endif
printk("\n");
ebp = *(unsigned long *)ebp;
}
__
Chuck
-
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