From: Anton Ivanov <antiv...@cisco.com>
This is a fix for a very old UML bug which can be triggered with stock
UML. It takes a lot of effort to trigger it there because the
lseek()/read() | write() mechanics of the UBD driver implicitly sync the
memory all the time by hitting the appropriate barrier implementation in
the host kernel.
By improving the disk susbsystem we make this bug raise its ugly head
with a vengeance - you can get a process in D (with an occasional child
in Z state) simply by running an apt-get on 30-40 large packages.
Is this correct place to have the sync - no idea. It may need to move
to somewhere inside tlb.c. With the fence in exec.c it works (TM).
If I understand this correctly, this also needs to be an instruction
appropriate for the underlying host so just a barrier() will not cut
it. You have to fence. En-guarde... Touche... :)
Signed-off-by: Anton Ivanov <antiv...@cisco.com>
---
arch/um/kernel/exec.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
index 0d7103c..7cb6805 100644
--- a/arch/um/kernel/exec.c
+++ b/arch/um/kernel/exec.c
@@ -27,6 +27,11 @@ void flush_thread(void)
ret = unmap(¤t->mm->context.id, 0, STUB_START, 0, &data);
ret = ret || unmap(¤t->mm->context.id, STUB_END,
host_task_size - STUB_END, 1, &data);
+#ifdef CONFIG_X86_32
+ alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2);
+#else
+ asm volatile("mfence":::"memory");
+#endif
if (ret) {
printk(KERN_ERR "flush_thread - clearing address space failed, "
"err = %d\n", ret);
--
1.7.10.4
------------------------------------------------------------------------------
Meet PCI DSS 3.0 Compliance Requirements with EventLog Analyzer
Achieve PCI DSS 3.0 Compliant Status with Out-of-the-box PCI DSS Reports
Are you Audit-Ready for PCI DSS 3.0 Compliance? Download White paper
Comply to PCI DSS 3.0 Requirement 10 and 11.5 with EventLog Analyzer
http://pubads.g.doubleclick.net/gampad/clk?id=154622311&iu=/4140/ostg.clktrk
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
