Re: possible deadlock in sys_pivot_root()?

Russell King (rmk@arm.linux.org.uk)
Mon, 27 Jan 2003 15:12:13 +0000

On Mon, Jan 27, 2003 at 05:12:27PM +0300, Nikita Danilov wrote:
> sys_pivot_root() first takes BKL, then ->i_sem on the old root
> directory. On the other hand, vfs_readdir() first takes ->i_sem on a
> directory and then calls file system ->readdir() method, that usually
> takes BKL. Isn't there a deadlock possibility? Of course,
> sys_pivot_root() is probably not supposed to be called frequently, but
> still.

No, you can't deadlock here. When you get contention on the i_sem,
one thread will be put to sleep, and when that happens, the BKL will
be automatically released.

So:

CPU0 CPU1

BKL
i_sem
BKL (spins, waiting for BKL to be released)

i_sem (finds it locked,
and sleeps, which
releases the BKL)
(BKL is now released, CPU1 continues)

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html


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