[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 <xyzzy@speakeasy.org>
Cc: Zwane Mwaikambo <zwane@fsmlabs.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Johannes Stezenbach <js@linuxtv.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 8 insertions, 7 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e1bd0842f6a1..f4fc576ed4c4 100644
--- a/include/linux/kernel.h
+++ b/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);
diff --git a/kernel/extable.c b/kernel/extable.c
index 7501b531ceed..7fe262855317 100644
--- a/kernel/extable.c
+++ b/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)
diff --git a/kernel/module.c b/kernel/module.c
index d24deb0dbbc9..bbe04862e1b0 100644
--- a/kernel/module.c
+++ b/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);