On 10/11/05, Tetsuo Handa <from-kernelnewbies@xxxxxxxxxxxxxxxxxxx> wrote: > Hello. > I posted this question 3 months ago, but I post again, for > I'm worried that this will cause a potential deadlock bug. Always worth asking this question because it provides an opportunity to recall why everything is ok. > Can a process do semaphore operations while the process is > holding a spinlock? No. Well, you might wake something up later. > As far as I know, a process must not call semaphore operations > nor functions that may sleep (such as kmalloc(GFP_KERNEL)) > when the process is holding a spinlock. That's right. To do so would be a really bad idea. > But I can find the following sequence. > > Step 1: lock_kernel() is called from sys_mount(). > ( at http://lxr.linux.no/source/fs/namespace.c?v=2.4.28#L855 ) Yes. The BKL is a magical super dooper uber ultra lock which violates *all* of the usual behaviours and can be called in contexts when you would normally not use a spinlock. It's an ugly hack that's slowly going away. > Why it is allowed to do semaphore operations (or kmalloc(GFP_KERNEL)) > while the kernel lock is held. Because the BKL is very special. > This will sleep and cause deadlock, won't this? No. The BKL gets silently released and reacquired without you noticing it is happening. Jon. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
