On Thu, May 01, 2014 at 11:42:52AM +0200, Miklos Szeredi wrote:
> Two points about latest version (dentry_kill-2):
>
> - Doing anything with dentry->d_parent in case of DCACHE_DENTRY_KILLED looks
> seriously wrong. Parent has been dealt with, at that point, by the other
> caller, no?
In both branches, actually - we should bugger off earlier *and* return NULL
in that case. Nice catch.
Hmm... I see why it failed to blow up on that. It *did* trigger, all right -
udev is stepping into that right on boot. The thing is, check should be
if ((int)dentry->d_lockref.count > 0)
since the damn thing is unsigned int. IOW, they did go through handover
and shrink_dentry_list() proceeded to lose them. And with that braino
fixed, it steps into the extra dput crap just fine.
OK, fixed and pushed (both branches).
> - "bool foo = flag & FLAG" looks suspicious. Is this guaranteed not to
> overflow?
What do you mean, overflow? It's not a 1-bit unsigned int; conversion to
_Bool is different (which is the only reason why it's more than mere
syntax sugar). See C99 6.3.2.1 ("When any scalar value is converted
to _Bool, the result is 0 if the value compares equal to 0; otherwise,
the result is 1").
That, BTW, is also the reason why _Bool bitfields exist - try
struct {
_Bool a:1;
unsigned b:1;
} x;
x.a = 2;
x.b = 2;
if (x.a)
printf("A");
if (x.b)
printf("B");
and see what it does. The first test triggers, same as if (2) would.
The second does not, since conversion to unsigned integer type other
than _Bool gives the value in range of that type comparable to original
modulo (maximal representable + 1). And 2 modulo 2 is 0...
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