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From:   David Howells <dhowells@redhat.com>
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To:     "Reshetova, Elena" <elena.reshetova@intel.com>
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Subject: Re: [PATCH 0/3] Convert nsproxy, groups, and creds to refcount_t
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Date:   Tue, 21 Jul 2020 12:02:19 +0100
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> https://github.com/ereshetova/linux-stable/commits/refcount_t_fs

Looking at "fs, cachefiles: convert cachefiles_object.usage from atomic_t =
to
refcount_t", I see:

-	u =3D atomic_inc_return(&object->usage);
+	refcount_inc(&object->usage);
	trace_cachefiles_ref(object, _object->cookie,
-			     (enum cachefiles_obj_ref_trace)why, u);
+			     (enum cachefiles_obj_ref_trace)why, refcount_read(&object->usage)=
);
	return &object->fscache;

This change is *not* equivalent.  There's a reason I'm using
atomic_inc_return() and not atomic_inc(),atomic_read().  Yes, the small wi=
ndow
*does* occasionally produce incorrect tracing, and, yes, when that happens=
 it
does make things confusing.

-	u =3D atomic_dec_return(&object->usage);
	trace_cachefiles_ref(object, _object->cookie,
-			     (enum cachefiles_obj_ref_trace)why, u);
-	ASSERTCMP(u, !=3D, -1);
-	if (u =3D=3D 0) {
+			     (enum cachefiles_obj_ref_trace)why, refcount_read(&object->usage)=
 - 1);
+	if (refcount_dec_and_test(&object->usage)) {

This is also not equivalent.  Again, there's a reason I'm using
atomic_dec_return() and not atomic_read(),atomic_dec_and_test().

So, please drop the cachefiles/fscache patches or use refcount_inc_return(=
)
and refcount_dec_return().

Another reason to please drop these patches is that they will cause my
fscache-iter branch to bounce.  A lot of this code is deleted/heavily
rewritten:

https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/=
?h=3Dfscache-iter

Thanks,
David