From: Dave Anderson <anderson@redhat.com>
Date: Fri, 26 Feb 2010 16:45:14 -0500
Subject: [mm] prevent severe performance degradation hang fix
Message-id: <1124585371.2423541267202714440.JavaMail.root@zmail05.collab.prod.int.phx2.redhat.com>
Patchwork-id: 23450
O-Subject: [RHEL5.5 PATCH] BZ #544448: update to "prevent severe performance
	degradation" patch
Bugzilla: 544448
RH-Acked-by: Rik van Riel <riel@redhat.com>

This is an add-on to the initial patch applied for this BZ:

 BZ #544448 - Strange vm performance degradation moving 32 bit app from
              RHEL 4.6 32bit to 5.4 64bit
 https://bugzilla.redhat.com/show_bug.cgi?id=544448

This is patch as posted on 1/28:

 [RHEL5-U5 Patch] prevent severe performance degradation of 32-bit apps running
                  on x86_64 that mmap() thousands of files.
 http://post-office.corp.redhat.com/archives/rhkernel-list/2010-January/msg01808.html

That patch implemented the arch_get_unmapped_area_topdown_fast() function.
QA testing of that patch uncovered a corner-case bug that can cause a task to
hang in the kernel forever.  If the topdown VMA search works its way down to
the bottom of the virtual address space such that the only remaining space:

 (1) precisely starts at user virtual address 0, and
 (2) fills up the virtual address space up from there to the starting
     address of the task's first VMA, then the function will loop forever.

Tested with the QA test and system parameters that showed the bug.

Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/arch/x86_64/kernel/sys_x86_64.c b/arch/x86_64/kernel/sys_x86_64.c
index e0b23f4..e24f562 100644
--- a/arch/x86_64/kernel/sys_x86_64.c
+++ b/arch/x86_64/kernel/sys_x86_64.c
@@ -287,7 +287,7 @@ try_again:
 
 		/* try just below the current vma->vm_start */
 		addr = vma->vm_start-len;
-	} while (len <= vma->vm_start);
+	} while (len < vma->vm_start);
 
 bottomup:
 	/*