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Date: Wed, 4 Jun 2003 15:48:28 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: linux-kernel@vger.kernel.org
Cc: Marcelo Tosatti <marcelo@conectiva.com.br>
Subject: shmctl(SHM_LOCK/UNLOCK) deadlock
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Hi,

this patch fixes an SMP deadlock that triggered in some production
usage:

--- xxx/mm/shmem.c.~1~	2003-06-01 19:14:07.000000000 +0200
+++ xxx/mm/shmem.c	2003-06-04 02:17:23.000000000 +0200
@@ -808,9 +808,9 @@ void shmem_lock(struct file * file, int 
 	struct inode * inode = file->f_dentry->d_inode;
 	struct shmem_inode_info * info = SHMEM_I(inode);
 
-	down(&info->sem);
+	spin_lock(&info->lock);
 	info->locked = lock;
-	up(&info->sem);
+	spin_unlock(&info->lock);
 }
 
 int shmem_make_bigpage_mmap(struct file * file, struct vm_area_struct * vma)

you can merge it in 21-final IMHO (even dropping the lock enterely would
been ok, the reader is out of order anyways and that's atomic stuff in C
no matter the architecture)

Andrea