[patch 5/10] mm: debug write deadlocks

[Nick Piggin]

Allow CONFIG_DEBUG_VM to switch off the prefaulting logic, to simulate the
difficult race where the page may be unmapped before calling copy_from_user.
Makes the race much easier to hit.

This is useful for demonstration and testing purposes, but is removed in a
subsequent patch.

Signed-off-by: Nick Piggin <[EMAIL PROTECTED]>

Index: linux-2.6/mm/filemap.c
===
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -1894,6 +1894,7 @@ generic_file_buffered_write(struct kiocb
if (maxlen > bytes)
maxlen = bytes;
 
+#ifndef CONFIG_DEBUG_VM
/*
 * Bring in the user page that we will copy from _first_.
 * Otherwise there's a nasty deadlock on copying from the
@@ -1901,6 +1902,7 @@ generic_file_buffered_write(struct kiocb
 * up-to-date.
 */
fault_in_pages_readable(buf, maxlen);
+#endif
 
page = __grab_cache_page(mapping,index,_page,_pvec);
if (!page) {
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[patch 5/10] mm: debug write deadlocks

[Nick Piggin]

Allow CONFIG_DEBUG_VM to switch off the prefaulting logic, to simulate the
difficult race where the page may be unmapped before calling copy_from_user.
Makes the race much easier to hit.

This is useful for demonstration and testing purposes, but is removed in a
subsequent patch.

Signed-off-by: Nick Piggin [EMAIL PROTECTED]

Index: linux-2.6/mm/filemap.c
===
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -1894,6 +1894,7 @@ generic_file_buffered_write(struct kiocb
if (maxlen  bytes)
maxlen = bytes;
 
+#ifndef CONFIG_DEBUG_VM
/*
 * Bring in the user page that we will copy from _first_.
 * Otherwise there's a nasty deadlock on copying from the
@@ -1901,6 +1902,7 @@ generic_file_buffered_write(struct kiocb
 * up-to-date.
 */
fault_in_pages_readable(buf, maxlen);
+#endif
 
page = __grab_cache_page(mapping,index,cached_page,lru_pvec);
if (!page) {
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/