Messages in this thread | | | Date | Wed, 17 Aug 2011 14:04:05 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 40/41] ncpfs: Use set_current_blocked() |
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On 08/16, Matt Fleming wrote: > > On Tue, 2011-08-16 at 19:56 +0200, Oleg Nesterov wrote: > > On 08/11, Matt Fleming wrote: > > > > > > As described in e6fa16ab ("signal: sigprocmask() should do > > > retarget_shared_pending()") the modification of current->blocked is > > > incorrect as we need to check whether the signal we're about to block > > > is pending in the shared queue. > > > > I'd wish I could understand this code but this seems impossible ;) > > Yeah, I gave up after staring at it for about twenty minutes. I couldn't > fathom the logic behind it. > > > IOW, "This doesn't seem right at all." looks reasonable, and the > > PF_EXITING adds even more confusion. > > Definitely. If I was more confident in this area of the kernel I would > have just deleted it ;-)
Same here ;)
> Because the thread doesn't hold ->siglock over do_ncp_rpc_call() another > thread could change the signal handler for SIGINT or SIGQUIT mid-call. > Which makes the code under "if (server->m.flags & NCP_MOUNT_INTR)" > pointless.
(indeed, and see below)
> > Why do we take ->siglock in the first place? > > > > I think it is not needed. We can calculate mask/blocked lockless and > > use set_task_blocked(). This also makes sense because __set_task_blocked > > is not exported ;) > > Eek! Sorry, I didn't realise this didn't compile. > > > the sighand->action[] checks are racy anyway in the mt case, siglock > > can't help. > > Hmm.. really? I thought that ->siglock serialised modifications to > sighand->action[] even in the mt case, no?
Sure. But another thread can change sighand->action[] right after we drop ->siglock. So how can this lock help? We simply read the word, this is atomic and doesn't need the locking.
Oleg.
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