Kanoj Sarcar wrote:

quoted

I think I put in the locks in the initial version of
the file becase the idea was that show_free_areas_node() could be 
invoked from any cpu
in a multinode system (via the sysrq keys or other
intr sources), and the spin lock would provide sanity in the print out. 

As Bill mentioned, a grep through the source shows that 
show_free_areas_node() is never called, and since it boils down to 
*just* a call to show_free_areas_core() w/out the locking, the revised 
patch pulls it out entirely.

quoted

For nonnuma discontig machines, isn't the spin lock
providing protection in the pgdat list chain walking
in _alloc_pages()?

Uhh...  kinda?  Since *next is static, it means that at best case, 2 
processes walking the pgdat_list chain will hip-hop over nodes...  If it 
is racy code, the *best* that lock is currently doing is making it mildy 
less racy, and at worst, hiding the fact that there is a race there.

I'm sure the lock was useful at some point, but it no longer is...  
Attatched is the new version, please apply..

Cheers!

-Matt

quoted

Kanoj

--- Matthew Dobson <colpatch@us.ibm.com> wrote:

quoted

There is a lock that is apparently protecting
nothing.  The node_lock spinlock in mm/numa.c is protecting read-only 
accesses to
pgdat_list.  Here is a patch to get rid of it.

Cheers!

-Matt

quoted

--- linux-2.5.26-vanilla/mm/numa.c    Tue Jul 16

16:49:30 2002

+++ linux-2.5.26-vanilla/mm/numa.c.fixed    Thu Jul 18

17:59:35 2002

@@ -44,15 +44,11 @@

#define LONG_ALIGN(x)
(((x)+(sizeof(long))-1)&~((sizeof(long))-1))

-static spinlock_t node_lock = SPIN_LOCK_UNLOCKED;
-
void show_free_areas_node(pg_data_t *pgdat)
{
    unsigned long flags;

-    spin_lock_irqsave(&node_lock, flags);
    show_free_areas_core(pgdat);
-    spin_unlock_irqrestore(&node_lock, flags);
}

/*

@@ -106,11 +102,9 @@

#ifdef CONFIG_NUMA
    temp = NODE_DATA(numa_node_id());
#else
-    spin_lock_irqsave(&node_lock, flags);
    if (!next) next = pgdat_list;
    temp = next;
    next = next->node_next;
-    spin_unlock_irqrestore(&node_lock, flags);
#endif
    start = temp;
    while (temp) {

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------------------------------------------------------------------------

--- linux-2.5.26-vanilla/mm/numa.c	Tue Jul 16 16:49:30 2002
+++ linux-2.5.26-vanilla/mm/numa.c.fixed	Thu Jul 18 17:59:35 2002

@@ -43,17 +43,6 @@
 #ifdef CONFIG_DISCONTIGMEM
 
 #define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))
-
-static spinlock_t node_lock = SPIN_LOCK_UNLOCKED;
-
-void show_free_areas_node(pg_data_t *pgdat)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&node_lock, flags);
-	show_free_areas_core(pgdat);
-	spin_unlock_irqrestore(&node_lock, flags);
-}
 
 /*
  * Nodes can be initialized parallely, in no particular order.

@@ -106,11 +103,9 @@
 #ifdef CONFIG_NUMA
 	temp = NODE_DATA(numa_node_id());
 #else
-	spin_lock_irqsave(&node_lock, flags);
 	if (!next) next = pgdat_list;
 	temp = next;
 	next = next->node_next;
-	spin_unlock_irqrestore(&node_lock, flags);
 #endif
 	start = temp;
 	while (temp) {