Re: [PATCH] 2.4: Restore current->files in flush_old_exec

[Herbert Xu]

On Sat, Aug 09, 2003 at 11:11:16AM +1000, herbert wrote:
> 
> At this point, I believe the unshare_files stuff should be fine from
> a correctness point of view.  However, there is still a performance
> problem as every ELF exec call ends up dupliating the files structure
> as well as walking through all file locks.

Here is the patch that ensures files is only duplicated when necessary.
-- 
Debian GNU/Linux 3.0 is out! ( http://www.debian.org/ )
Email:  Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--- kernel-source-2.4/fs/binfmt_elf.c.orig	2003-08-09 11:28:18.000000000 +1000
+++ kernel-source-2.4/fs/binfmt_elf.c	2003-08-09 11:32:13.000000000 +1000
@@ -480,6 +480,10 @@
 	files = current->files;		/* Refcounted so ok */
 	if(unshare_files() < 0)
 		goto out_free_ph;
+	if (files == current->files) {
+		put_files_struct(files);
+		files = NULL;
+	}
 
 	/* exec will make our files private anyway, but for the a.out
 	   loader stuff we need to do it earlier */
@@ -602,8 +606,10 @@
 		goto out_free_dentry;
 
 	/* Discard our unneeded old files struct */
-	steal_locks(files, current->files);
-	put_files_struct(files);
+	if (files) {
+		steal_locks(files, current->files);
+		put_files_struct(files);
+	}
 
 	/* OK, This is the point of no return */
 	current->mm->start_data = 0;
@@ -811,9 +817,11 @@
 out_free_file:
 	sys_close(elf_exec_fileno);
 out_free_fh:
-	ftmp = current->files;
-	current->files = files;
-	put_files_struct(ftmp);
+	if (files) {
+		ftmp = current->files;
+		current->files = files;
+		put_files_struct(ftmp);
+	}
 out_free_ph:
 	kfree(elf_phdata);
 	goto out;