Re: [PATCH] [1/2] random: SMP locking

From: Matt Mackall (mpm@selenic.com)
Date: Sat Aug 02 2003 - 13:42:27 EST

On Sat, Aug 02, 2003 at 08:35:22AM -0400, Zwane Mwaikambo wrote:
> On Sat, 2 Aug 2003, Andrew Morton wrote:
>
> > Cannot perform userspace access while holding a lock - a pagefault could
> > occur, perform IO, schedule away and the same CPU tries to take the same
> > lock via a different process.
>
> Perhaps might_sleep() in *_user, copy_* etc is in order?

I think it's been suggested before, but I threw a patch together for
i386 anyway.

This only checks in the non-__ versions, as those are occassionally
called inside things like kmap_atomic pairs which take a spinlock in
with highmem. It's all conditional on CONFIG_DEBUG_SPINLOCK_SLEEP
(which isn't quite the right name) so there's no overhead for normal
builds.

diff -urN -X dontdiff orig/arch/i386/lib/usercopy.c work/arch/i386/lib/usercopy.c
--- orig/arch/i386/lib/usercopy.c 2003-07-13 22:28:54.000000000 -0500
+++ work/arch/i386/lib/usercopy.c 2003-08-02 13:33:43.000000000 -0500
@@ -149,6 +149,7 @@
 unsigned long
 clear_user(void __user *to, unsigned long n)
 {
+ might_sleep();
         if (access_ok(VERIFY_WRITE, to, n))
                 __do_clear_user(to, n);
         return n;
@@ -188,6 +189,8 @@
         unsigned long mask = -__addr_ok(s);
         unsigned long res, tmp;
 
+ might_sleep();
+
         __asm__ __volatile__(
                 " testl %0, %0\n"
                 " jz 3f\n"
diff -urN -X dontdiff orig/include/asm-i386/uaccess.h work/include/asm-i386/uaccess.h
--- orig/include/asm-i386/uaccess.h 2003-07-13 22:30:48.000000000 -0500
+++ work/include/asm-i386/uaccess.h 2003-08-02 13:15:42.000000000 -0500
@@ -260,6 +260,7 @@
 ({ \
         long __pu_err = -EFAULT; \
         __typeof__(*(ptr)) *__pu_addr = (ptr); \
+ might_sleep(); \
         if (access_ok(VERIFY_WRITE,__pu_addr,size)) \
                 __put_user_size((x),__pu_addr,(size),__pu_err,-EFAULT); \
         __pu_err; \
@@ -469,6 +470,7 @@
 static inline unsigned long
 copy_to_user(void __user *to, const void *from, unsigned long n)
 {
+ might_sleep();
         if (access_ok(VERIFY_WRITE, to, n))
                 n = __copy_to_user(to, from, n);
         return n;
@@ -493,6 +495,7 @@
 static inline unsigned long
 copy_from_user(void *to, const void __user *from, unsigned long n)
 {
+ might_sleep();
         if (access_ok(VERIFY_READ, from, n))
                 n = __copy_from_user(to, from, n);
         else 

-- 
Matt Mackall : http://www.selenic.com : of or relating to the moon
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This archive was generated by hypermail 2b29 : Thu Aug 07 2003 - 22:00:19 EST