bad refcounting in nsCodebasePrincipal

VERIFIED WORKSFORME

Status

()

Core
Security
P3
normal
VERIFIED WORKSFORME
18 years ago
18 years ago

People

(Reporter: Warren Harris, Assigned: Norris Boyd)

Tracking

Trunk
x86
Windows NT
Points:
---
Dependency tree / graph

Firefox Tracking Flags

(Not tracked)

Details

(Reporter)

Description

18 years ago
Bloaty: Refcounting and Memory Bloat
Statistics

|<-------Name------>|<--------------References-------------->|<----------------
Objects---------------->|<------Size----->|
                               Rem    Total      Mean       StdDev       Rem
Total      Mean       StdDev Per-Class      Rem
  78 nsCodebasePrincipal        -3      258 (   -1.33 +/-     1.90)        1
5 (    0.56 +/-     0.83)       36       36

Norris,

I suspect that the refcount is going negative on this class because the mRefCnt
field isn't really being used, and the mJSPrincipals.refcount field is instead.
Maybe somewhere along the way, the nsCodebasePrincipal is getting QI'd to
nsISupports and that's incrementing the other mRefCnt(?). I couldn't catch it
in the act.

We really should fix this so that it doesn't get in the way of tracking down
other refcounting problems.

Warren
(Assignee)

Comment 1

18 years ago
Do you have any test case that reproduces this?
(Assignee)

Comment 2

18 years ago
There's only one vtable pointer in the nsCodebasePrincipal object, and it points
to the overridden forms of AddRef and Release. So a QI should never result in an
object whose AddRef and Release affect nsISupports::mRefCnt.
(Reporter)

Comment 3

18 years ago
Ok, well I guess that theory's wrong. But I got this by recompiling with BLOATY
defined in nsISupportsUtil.h and visiting www.mozilla.org, www.yahoo.com and
then drilling down into the yahoo site for several pages. I'll try to reproduce
it again later today.
(Assignee)

Updated

18 years ago
Status: NEW → ASSIGNED
(Assignee)

Comment 4

18 years ago
I just checked in changes to assert if Release or AddRef of a
nsCodebasePrincipal is called with a mRefcnt != 0. We'll see if anyone else can
reproduce this problem.
(Reporter)

Comment 5

18 years ago
Well, that's not really what I had in mind when filing this bug. I'd like to
see you fix the bloat statistics to reflect reality so that people won't think
that nsCodebasePrincipals are leaking. The statistics can get off if
the NS_IMPL_ADDREF/RELEASE macros aren't used, or if the
NS_LOG_ADDREF/NS_LOG_RELEASE macros aren't used consistently in hand-written
AddRef/Release implementations. The statistics can also get off if there's a
real leak.

Also, I'm not sure your assertion is useful for the case where the
nsCodebasePrincipal isn't getting released/destroyed.
(Assignee)

Updated

18 years ago
Depends on: 16466
(Assignee)

Comment 6

18 years ago
I tried turning on the about:bloat code to look at the nsCodebasePrincipal
refcounts. I tried loading www.mozilla.org, then www.yahoo.com, and then going
down several layers deep into yahoo. I never saw any negative refcounts in the
about:bloat page.

I did see leaks of nsDocuments, which are holding refs to nsCodebasePrincipals
and preventing them from being released. I've filed bug 16466 on that. When that
bug is resolved, I'll ensure again that nsCodebasePrincipals are indeed released
after the associated page goes away.
(Reporter)

Comment 7

18 years ago
Ok, I can't reproduce this now either. Maybe something else got fixed and
cleared it up. Maybe we should mark it WORKSFORME.
(Assignee)

Updated

18 years ago
Status: ASSIGNED → RESOLVED
Last Resolved: 18 years ago
Resolution: --- → WORKSFORME
(Assignee)

Comment 8

18 years ago
Done. Thanks for retrying.

Updated

18 years ago
Blocks: 16654

Comment 9

18 years ago
Verified worksforme.
Status: RESOLVED → VERIFIED
QA Contact: dshea → junruh

Comment 10

18 years ago
Bulk moving all Browser Security bugs to new Security: General component.  The 
previous Security component for Browser will be deleted.
Component: Security → Security: General
You need to log in before you can comment on or make changes to this bug.