__vmalloc with GFP_ATOMIC causes 'sleeping from invalid context'

[Giridhar Pemmasani <giri@lmc.cs.sunysb.edu>]

If __vmalloc is called in atomic context with GFP_ATOMIC flags,
__get_vm_area_node is called, which calls kmalloc_node with GFP_KERNEL
flags. This causes 'sleeping function called from invalid context at
mm/slab.c:2729' with 2.6.16-rc4 kernel. A simple solution is to use
proper flags in __get_vm_area_node, depending on the context:

diff -Naur linux.orig/mm/vmalloc.c linux/mm/vmalloc.c
--- linux.orig/mm/vmalloc.c	2006-05-19 01:22:00.000000000 -0400
+++ linux/mm/vmalloc.c	2006-05-19 01:53:05.000000000 -0400
@@ -177,7 +177,10 @@
 	addr = ALIGN(start, align);
 	size = PAGE_ALIGN(size);
 
-	area = kmalloc_node(sizeof(*area), GFP_KERNEL, node);
+	if (in_atomic() || in_interrupt())
+		area = kmalloc_node(sizeof(*area), GFP_ATOMIC, node);
+	else
+		area = kmalloc_node(sizeof(*area), GFP_KERNEL, node);
 	if (unlikely(!area))
 		return NULL;
 

An alternate solution is to pass flags to __get_vm_area_node what was
passed to __vmalloc so it can call kmalloc_node with either GFP_KERNEL
or GFP_ATOMIC, but that changes signature of get_vm_area_node and
__get_vm_area_node which may affect other parts of kernel / modules.

Another point: In include/linux/kernel.h, might_resched() is defined
as

#ifdef CONFIG_PREEMPT_VOLUNTARY
extern int cond_resched(void);
# define might_resched() cond_resched()
#else
# define might_resched() do { } while (0)
#endif

Why is cond_resched() used only if CONFIG_PREEMPT_VOLUNTARY and not if
CONFIG_PREEMPT is enabled? i.e., shouldn't it be defined as

#if defined(CONFIG_PREEMPT_VOLUNTARY) || defined(CONFIG_PREEMPT)
extern int cond_resched(void);
# define might_resched() cond_resched()
#else
# define might_resched() do { } while (0)
#endif

Thanks,
Giri
-
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