[PATCH] symbol_put_addr() locks kernel

Even since a previous patch:

Fix race between CONFIG_DEBUG_SLABALLOC and modules
Sun, 27 Jun 2004 17:55:19 +0000 (17:55 +0000)
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commit;h=92b3db26d31cf21b70e3c1eadc56c179506d8fbe

The function symbol_put_addr() will deadlock the kernel.

symbol_put_addr() would acquire modlist_lock, then while holding the lock call
two functions kernel_text_address() and module_text_address() which also try
to acquire the same lock.  This deadlocks the kernel of course.

This patch changes symbol_put_addr() to not acquire the modlist_lock, it
doesn't need it since it never looks at the module list directly.  Also, it
now uses core_kernel_text() instead of kernel_text_address().  The latter has
an additional check for addr inside a module, but we don't need to do that
since we call module_text_address() (the same function kernel_text_address
uses) ourselves.

Signed-off-by: Trent Piepho <[email protected]>
Cc: Zwane Mwaikambo <[email protected]>
Acked-by: Rusty Russell <[email protected]>
Cc: Johannes Stezenbach <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/kernel.h

@@ -124,6 +124,7 @@ extern int get_option(char **str, int *pint);
 extern char *get_options(const char *str, int nints, int *ints);
 extern unsigned long long memparse(char *ptr, char **retptr);
 
+extern int core_kernel_text(unsigned long addr);
 extern int __kernel_text_address(unsigned long addr);
 extern int kernel_text_address(unsigned long addr);
 extern int session_of_pgrp(int pgrp);

kernel/extable.c

@@ -40,7 +40,7 @@ const struct exception_table_entry *search_exception_tables(unsigned long addr)
 	return e;
 }
 
-static int core_kernel_text(unsigned long addr)
+int core_kernel_text(unsigned long addr)
 {
 	if (addr >= (unsigned long)_stext &&
 	    addr <= (unsigned long)_etext)

kernel/module.c

@@ -705,14 +705,14 @@ EXPORT_SYMBOL(__symbol_put);
 
 void symbol_put_addr(void *addr)
 {
-	unsigned long flags;
+	struct module *modaddr;
 
-	spin_lock_irqsave(&modlist_lock, flags);
-	if (!kernel_text_address((unsigned long)addr))
-		BUG();
+	if (core_kernel_text((unsigned long)addr))
+		return;
 
-	module_put(module_text_address((unsigned long)addr));
-	spin_unlock_irqrestore(&modlist_lock, flags);
+	if (!(modaddr = module_text_address((unsigned long)addr)))
+		BUG();
+	module_put(modaddr);
 }
 EXPORT_SYMBOL_GPL(symbol_put_addr);