[PATCH] i386: fix file_read_actor() and pipe_read() for original i386 systems
The __copy_to_user_inatomic() calls in file_read_actor() and pipe_read()
are broken on original i386 machines, where WP-works-ok == false, as
__copy_to_user_inatomic() on such systems calls functions which might
sleep and/or contain cond_resched() calls inside of a kmap_atomic()
region.
The original check for WP-works-ok was in access_ok(), but got moved
during the 2.5 series to fix a race vs. swap.
Return the number of bytes to copy in the case where we are in an atomic
region, so the non atomic code pathes in file_read_actor() and
pipe_read() are taken.
This could be optimized to avoid the kmap_atomicby moving the check for
WP-works-ok into fault_in_pages_writeable(), but this is more intrusive
and can be done later.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/i386/lib/usercopy.c b/arch/i386/lib/usercopy.c
index d22cfc9..086b372 100644
--- a/arch/i386/lib/usercopy.c
+++ b/arch/i386/lib/usercopy.c
@@ -10,6 +10,7 @@
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
+#include <linux/interrupt.h>
#include <asm/uaccess.h>
#include <asm/mmx.h>
@@ -719,6 +720,14 @@
#ifndef CONFIG_X86_WP_WORKS_OK
if (unlikely(boot_cpu_data.wp_works_ok == 0) &&
((unsigned long )to) < TASK_SIZE) {
+ /*
+ * When we are in an atomic section (see
+ * mm/filemap.c:file_read_actor), return the full
+ * length to take the slow path.
+ */
+ if (in_atomic())
+ return n;
+
/*
* CPU does not honor the WP bit when writing
* from supervisory mode, and due to preemption or SMP,