Re: highmem deadlock fix [was Re: VM in 2.4.10(+tweaks) vs.

[Linus Torvalds]

On Thu, 27 Sep 2001, Linus Torvalds wrote:
>
> Thinking about it, I think GFP_NOIO also implies "we must not wait for
> other buffers", because that could deadlock for _other_ things too, like
> loop and NBD (which use NOIO to make sure that they don't recurse - but
> that should also imply not waiting for themselves). The GFP_xxx approach
> should fix those deadlocks too.

Ie the patch would be something like the attached..

		Linus

------
diff -u --recursive --new-file v2.4.10/linux/fs/buffer.c linux/fs/buffer.c
--- v2.4.10/linux/fs/buffer.c	Wed Sep 26 11:53:42 2001
+++ linux/fs/buffer.c	Thu Sep 27 16:13:47 2001
@@ -2522,7 +2373,7 @@
 					ll_rw_block(WRITE, 1, &p);
 					tryagain = 0;
 				} else if (buffer_locked(p)) {
-					if (gfp_mask & __GFP_WAIT) {
+					if (gfp_mask & __GFP_WAITBUF) {
 						wait_on_buffer(p);
 						tryagain = 1;
 					} else
diff -u --recursive --new-file v2.4.10/linux/include/linux/mm.h linux/include/linux/mm.h
--- v2.4.10/linux/include/linux/mm.h	Sun Sep 23 11:41:01 2001
+++ linux/include/linux/mm.h	Thu Sep 27 16:13:35 2001
@@ -550,16 +550,17 @@
 #define __GFP_IO	0x40	/* Can start low memory physical IO? */
 #define __GFP_HIGHIO	0x80	/* Can start high mem physical IO? */
 #define __GFP_FS	0x100	/* Can call down to low-level FS? */
+#define __GFP_WAITBUF	0x200	/* Can we wait for buffers to complete? */

 #define GFP_NOHIGHIO	(__GFP_HIGH | __GFP_WAIT | __GFP_IO)
 #define GFP_NOIO	(__GFP_HIGH | __GFP_WAIT)
-#define GFP_NOFS	(__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_HIGHIO)
+#define GFP_NOFS	(__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_WAITBUF)
 #define GFP_ATOMIC	(__GFP_HIGH)
-#define GFP_USER	(             __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_FS)
-#define GFP_HIGHUSER	(             __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_FS | __GFP_HIGHMEM)
-#define GFP_KERNEL	(__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_FS)
-#define GFP_NFS		(__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_FS)
-#define GFP_KSWAPD	(             __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_FS)
+#define GFP_USER	(             __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_WAITBUF | __GFP_FS)
+#define GFP_HIGHUSER	(             __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_WAITBUF | __GFP_FS | __GFP_HIGHMEM)
+#define GFP_KERNEL	(__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_WAITBUF | __GFP_FS)
+#define GFP_NFS		(__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_WAITBUF | __GFP_FS)
+#define GFP_KSWAPD	(             __GFP_WAIT | __GFP_IO | __GFP_HIGHIO | __GFP_WAITBUF | __GFP_FS)

 /* Flag - indicates that the buffer will be suitable for DMA.  Ignored on some
    platforms, used as appropriate on others */