diff options
| author | Ingo Molnar <mingo@elte.hu> | 2007-10-19 12:19:26 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2007-11-05 09:56:07 -0800 |
| commit | e2b35e3aaf9f6e140a56aba85aca84463a3d16c4 (patch) | |
| tree | c722c5842387e6d372509f709416e5571cfa7344 | |
| parent | b5f591838db12ca39e25b70278beec499fa56751 (diff) | |
x86: fix global_flush_tlb() bug
patch 9a24d04a3c26c223f22493492c5c9085b8773d4a upstream
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>
Cc: Andi Kleen <ak@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -rw-r--r-- | arch/x86_64/mm/pageattr.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86_64/mm/pageattr.c b/arch/x86_64/mm/pageattr.c index 9148f4a4cec..7cd5254d296 100644 --- a/arch/x86_64/mm/pageattr.c +++ b/arch/x86_64/mm/pageattr.c @@ -227,9 +227,14 @@ 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); |