Re: frequent lockups in 3.18rc4

From: Linus Torvalds
Date: Sat Dec 13 2014 - 18:10:18 EST

On Sat, Dec 13, 2014 at 2:59 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> The generic code does that mnt_want_write/mnt_drop_write
> dance adound the call to setxattr, and that in turn does
> while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
> cpu_relax();
> with preemption explicitly disabled.

Btw, I see no reason why mnt_want_write/mnt_drop_write disables
preemption. They don't care, they just care about the ordering of the
write counts and the MNT_WRITE_HOLD bit. It's the code that sets the
bit that should care, afaik. But maybe I'm missing something.

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