diff options
author | Ingo Molnar <mingo@elte.hu> | 2007-10-19 12:19:26 +0200 |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2007-10-19 12:19:26 +0200 |
commit | 9a24d04a3c26c223f22493492c5c9085b8773d4a (patch) | |
tree | 2c541bdeac1f11973ab4fbde5f7c19024c4fecfe | |
parent | 4fa4d23fa20de67df919030c1216295664866ad7 (diff) |
x86: fix global_flush_tlb() bug
While we were reviewing pageattr_32/64.c for unification,
Thomas Gleixner noticed the following serious SMP bug in
global_flush_tlb():
down_read(&init_mm.mmap_sem);
list_replace_init(&deferred_pages, &l);
up_read(&init_mm.mmap_sem);
this is SMP-unsafe because list_replace_init() done on two CPUs in
parallel can corrupt the list.
This bug has been introduced about a year ago in the 64-bit tree:
commit ea7322decb974a4a3e804f96a0201e893ff88ce3
Author: Andi Kleen <ak@suse.de>
Date: Thu Dec 7 02:14:05 2006 +0100
[PATCH] x86-64: Speed and clean up cache flushing in change_page_attr
down_read(&init_mm.mmap_sem);
- dpage = xchg(&deferred_pages, NULL);
+ list_replace_init(&deferred_pages, &l);
up_read(&init_mm.mmap_sem);
the xchg() based version was SMP-safe, but list_replace_init() is not.
So this "cleanup" introduced a nasty bug.
why this bug never become prominent is a mystery - it can probably be
explained with the (still) relative obscurity of the x86_64 architecture.
the safe fix for now is to write-lock init_mm.mmap_sem.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r-- | arch/x86/mm/pageattr_64.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/mm/pageattr_64.c b/arch/x86/mm/pageattr_64.c index 8a4f65bf956e..c7b7dfe1d405 100644 --- a/arch/x86/mm/pageattr_64.c +++ b/arch/x86/mm/pageattr_64.c @@ -230,9 +230,14 @@ void global_flush_tlb(void) struct page *pg, *next; struct list_head l; - down_read(&init_mm.mmap_sem); + /* + * Write-protect the semaphore, to exclude two contexts + * doing a list_replace_init() call in parallel and to + * exclude new additions to the deferred_pages list: + */ + down_write(&init_mm.mmap_sem); list_replace_init(&deferred_pages, &l); - up_read(&init_mm.mmap_sem); + up_write(&init_mm.mmap_sem); flush_map(&l); |