[Patch] Do not copy from remote while in_atomic()

Here is a patch for CONFIG_HIGHMEM enabled kernels. 

Some kernel functions use kmap_atomic() rather than kmap() to map a
page before copying data from user space. While this is faster, atomic
maps pose a problem with OpenMosix: deputy_copy_from_user() has to
get the data over the network; the network code in turn might
reschedule, which will lead to a "scheduling while atomic" error
message. Worse, the copied data may be corrupted.
One of the functions affected is the write() system call.

The following patch makes deputy_copy_*_user() fail gracefully in this
case. The calling function then has the opportunity to retry the
operation using non-atomic maps instead.


A.



diff -ruNp linux-2.6-om/hpc/copyuser.c linux-2.6-om-work/hpc/copyuser.c
--- linux-2.6-om/hpc/copyuser.c	2006-02-07 16:51:58.000000000 +0100
+++ linux-2.6-om-work/hpc/copyuser.c	2006-03-22 15:43:52.000000000 +0100
@@ -27,6 +27,9 @@ unsigned long deputy_copy_from_user(void
 {
 	struct omp_usercopy_req u;
 	int error;
+
+	if (in_atomic())
+		return n;
 	
 	u.addr = (unsigned long) from;
 	u.len = n;
@@ -82,6 +85,9 @@ unsigned long deputy_copy_to_user(void _
 {
 	struct omp_usercopy_req u;
 	int error;
+
+	if (in_atomic())
+		return n;
 	
 	OMDEBUG_CPYUSER(1, "copy [0x%p]->user[0x%p][%ld]\n", from, to, n);
 	u.addr = (unsigned long) to;


-- 
Ansgar Esztermann
Researcher & Sysadmin
http://www2.thphy.uni-duesseldorf.de/~ansgar

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