poma <pomidorabelisima@xxxxxxxxx> writes: >> Ref. >> https://bugzilla.redhat.com/show_bug.cgi?id=1252167 >> https://bugzilla.kernel.org/show_bug.cgi?id=102631 >> > > You guys are really something. Hi Poma, I understand your frustration! I got involved via the other thread which didn't mention your bug report anywhere. I'm sure Laura was trying to be helpful by creating a minimal report, but the resulting patch erred in not crediting you. > First of all, as is evident here, I am the original reporter, not Laura Abbott <labbott@xxxxxxxxxx>. Thanks for clarifying that. I have fixed the commit message to credit you. See below. > -All- your comments including the final patch on this issue, are just plain wrong.[1] > > This patch only hides the actual problem with this particular device - the dual tuner combination driven by dvb_usb_af9015 & mxl5007t, broken by design since day one. Oh, there's definitely a real issue in the driver; this one is cosmetic. > Read the entire https://bugzilla.redhat.com/show_bug.cgi?id=1252167 > and stop this nonsense. > > NACK "module: Fix locking in symbol_put_addr()" Yeah, I've had days like this, too :( Anyway, thanks for finding this bug: if the driver init hadn't been screwed it wouldn't have taken that path and found this for us. Good luck with the other issue! Rusty. >From 275d7d44d802ef271a42dc87ac091a495ba72fc5 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Date: Thu, 20 Aug 2015 10:34:59 +0930 Subject: [PATCH] module: Fix locking in symbol_put_addr() 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@xxxxxxxxxx> 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@xxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx> Fixes: a6e6abd575fc ("module: remove module_text_address()") Cc: stable@xxxxxxxxxx diff --git a/kernel/module.c b/kernel/module.c index b86b7bf1be38..8f051a106676 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -1063,11 +1063,15 @@ 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); -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
