On Sat, Oct 25, 2014 at 11:53:52AM +0200, Miklos Szeredi wrote:
> Yes, but it's not about race with copy-up (which the ovl_path_upper()
> protects against), but race of two fsync calls with each other. If
> there's no synchronization between them, then that od->upperfile does
> indeed count as lockless access, no matter that the assignment was
> done under lock.
p = global;
if (!p) { // outside of lock
p = alloc();
grab lock
if (!global) {
global = p;
} else {
destroy(p);
p = global;
}
drop lock
}
is a very common pattern, especially if you look for cases when lock is
a spinlock and allocation is blocking (in those cases you'll often see
destroy() part done after dropping the lock; that's where what I fucked up in
what I'd originally pushed. And it wasn't even needed - fput() under
->i_mutex is OK...)
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