| From 275d7d44d802ef271a42dc87ac091a495ba72fc5 Mon Sep 17 00:00:00 2001 |
| From: Peter Zijlstra <peterz@infradead.org> |
| Date: Thu, 20 Aug 2015 10:34:59 +0930 |
| Subject: module: Fix locking in symbol_put_addr() |
| |
| commit 275d7d44d802ef271a42dc87ac091a495ba72fc5 upstream. |
| |
| Poma (on the way to another bug) reported an assertion triggering: |
| |
| [<ffffffff81150529>] module_assert_mutex_or_preempt+0x49/0x90 |
| [<ffffffff81150822>] __module_address+0x32/0x150 |
| [<ffffffff81150956>] __module_text_address+0x16/0x70 |
| [<ffffffff81150f19>] symbol_put_addr+0x29/0x40 |
| [<ffffffffa04b77ad>] dvb_frontend_detach+0x7d/0x90 [dvb_core] |
| |
| Laura Abbott <labbott@redhat.com> produced a patch which lead us to |
| inspect symbol_put_addr(). This function has a comment claiming it |
| doesn't need to disable preemption around the module lookup |
| because it holds a reference to the module it wants to find, which |
| therefore cannot go away. |
| |
| This is wrong (and a false optimization too, preempt_disable() is really |
| rather cheap, and I doubt any of this is on uber critical paths, |
| otherwise it would've retained a pointer to the actual module anyway and |
| avoided the second lookup). |
| |
| While its true that the module cannot go away while we hold a reference |
| on it, the data structure we do the lookup in very much _CAN_ change |
| while we do the lookup. Therefore fix the comment and add the |
| required preempt_disable(). |
| |
| Reported-by: poma <pomidorabelisima@gmail.com> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> |
| Fixes: a6e6abd575fc ("module: remove module_text_address()") |
| Signed-off-by: Zefan Li <lizefan@huawei.com> |
| --- |
| kernel/module.c | 8 ++++++-- |
| 1 file changed, 6 insertions(+), 2 deletions(-) |
| |
| --- a/kernel/module.c |
| +++ b/kernel/module.c |
| @@ -887,11 +887,15 @@ void symbol_put_addr(void *addr) |
| if (core_kernel_text(a)) |
| return; |
| |
| - /* module_text_address is safe here: we're supposed to have reference |
| - * to module from symbol_get, so it can't go away. */ |
| + /* |
| + * Even though we hold a reference on the module; we still need to |
| + * disable preemption in order to safely traverse the data structure. |
| + */ |
| + preempt_disable(); |
| modaddr = __module_text_address(a); |
| BUG_ON(!modaddr); |
| module_put(modaddr); |
| + preempt_enable(); |
| } |
| EXPORT_SYMBOL_GPL(symbol_put_addr); |
| |