From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: David Vernet <void@manifault.com>
Cc: Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
linux-doc@vger.kernel.org, live-patching@vger.kernel.org,
linux-kernel@vger.kernel.org, jpoimboe@redhat.com,
jikos@kernel.org, joe.lawrence@redhat.com, corbet@lwn.net,
yhs@fb.com, songliubraving@fb.com
Subject: Re: [PATCH] livepatch: Fix leak on klp_init_patch_early failure path
Date: Tue, 14 Dec 2021 16:50:15 +0100 [thread overview]
Message-ID: <Ybi9NzbvWU7ka8m1@kroah.com> (raw)
In-Reply-To: <Ybi3qcA5ySDYpyib@dev0025.ash9.facebook.com>
On Tue, Dec 14, 2021 at 07:26:33AM -0800, David Vernet wrote:
> Miroslav Benes <mbenes@suse.cz> wrote on Tue [2021-Dec-14 10:17:08 +0100]:
> > It would help to share warning outputs (or whatever) from DEBUG_KOBJECTS.
>
> This is the output when running kpatch load livepatch-sample.ko if an extra
> 'struct klp_obj' entry is added that has a name but no funcs:
>
> Without patch:
>
> [ 67.285762] livepatch_sample: tainting kernel with TAINT_LIVEPATCH
> [ 67.286107] kobject: 'livepatch_sample' (00000000cf89f7b6): kobject_add_internal: parent: 'module', set: 'module'
> [ 67.286113] kobject: 'holders' (00000000858b03bf): kobject_add_internal: parent: 'livepatch_sample', set: '<NULL>'
> [ 67.286126] kobject: 'notes' (00000000f2a3a4ce): kobject_add_internal: parent: 'livepatch_sample', set: '<NULL>'
> [ 67.297856] kobject: 'holders' (00000000858b03bf): kobject_cleanup, parent 00000000cf89f7b6
> [ 67.297859] kobject: 'holders' (00000000858b03bf): auto cleanup kobject_del
> [ 67.297861] kobject: 'holders' (00000000858b03bf): calling ktype release
> [ 67.297862] kobject: (00000000858b03bf): dynamic_kobj_release
> [ 67.297863] kobject: 'holders': free name
> [ 67.297865] kobject: 'notes' (00000000f2a3a4ce): kobject_cleanup, parent 00000000cf89f7b6
> [ 67.297866] kobject: 'notes' (00000000f2a3a4ce): auto cleanup kobject_del
> [ 67.297867] kobject: 'notes' (00000000f2a3a4ce): calling ktype release
> [ 67.297868] kobject: (00000000f2a3a4ce): dynamic_kobj_release
> [ 67.297869] kobject: 'notes': free name
> [ 67.297874] kobject: 'livepatch_sample' (00000000cf89f7b6): kobject_cleanup, parent 000000002555fa2d
> [ 67.297876] kobject: 'livepatch_sample' (00000000cf89f7b6): auto cleanup kobject_del
> [ 67.297877] kobject: 'livepatch_sample' (00000000cf89f7b6): calling ktype release
> [ 67.297878] kobject: 'livepatch_sample': free name
> [ 99.445938] kobject: '0:40' (000000002a98d11d): kobject_add_internal: parent: 'bdi', set: 'devices'
> [ 99.445954] kobject: '0:40' (000000002a98d11d): kobject_uevent_env
> [ 99.445957] kobject: '0:40' (000000002a98d11d): fill_kobj_path: path = '/devices/virtual/bdi/0:40'
>
> With patch:
>
> [ 162.275251] livepatch_sample: tainting kernel with TAINT_LIVEPATCH
> [ 162.275985] kobject: 'livepatch_sample' (00000000e688ee30): kobject_add_internal: parent: 'module', set: 'module'
> [ 162.275993] kobject: 'holders' (000000004eee7860): kobject_add_internal: parent: 'livepatch_sample', set: '<NULL>'
> [ 162.276010] kobject: 'notes' (00000000c4f390ab): kobject_add_internal: parent: 'livepatch_sample', set: '<NULL>'
> [ 162.276028] kobject: '(null)' (000000003acccf72): kobject_cleanup, parent 0000000000000000
> [ 162.276031] kobject: '(null)' (000000003acccf72): calling ktype release
> [ 162.276033] kobject: '(null)' (00000000aeae6326): kobject_cleanup, parent 0000000000000000
> [ 162.276035] kobject: '(null)' (00000000aeae6326): calling ktype release
> [ 162.276037] kobject: '(null)' (0000000093b68297): kobject_cleanup, parent 0000000000000000
> [ 162.276039] kobject: '(null)' (0000000093b68297): calling ktype release
> [ 162.294063] kobject: 'holders' (000000004eee7860): kobject_cleanup, parent 00000000e688ee30
> [ 162.294070] kobject: 'holders' (000000004eee7860): auto cleanup kobject_del
> [ 162.294074] kobject: 'holders' (000000004eee7860): calling ktype release
> [ 162.294078] kobject: (000000004eee7860): dynamic_kobj_release
> [ 162.294081] kobject: 'holders': free name
> [ 162.294086] kobject: 'notes' (00000000c4f390ab): kobject_cleanup, parent 00000000e688ee30
> [ 162.294090] kobject: 'notes' (00000000c4f390ab): auto cleanup kobject_del
> [ 162.294094] kobject: 'notes' (00000000c4f390ab): calling ktype release
> [ 162.294097] kobject: (00000000c4f390ab): dynamic_kobj_release
> [ 162.294100] kobject: 'notes': free name
> [ 162.294114] kobject: 'livepatch_sample' (00000000e688ee30): kobject_cleanup, parent 00000000f9317c72
> [ 162.294118] kobject: 'livepatch_sample' (00000000e688ee30): auto cleanup kobject_del
> [ 162.294123] kobject: 'livepatch_sample' (00000000e688ee30): calling ktype release
> [ 162.294126] kobject: 'livepatch_sample': free name
>
> The extra lines are of course the kobject: '(null)' entries, for which we
> *don't* see auto cleanup kobject_del being called. So it seems that what's
> there now is probably not actually leaking memory, and the question is
> really whether or not the documentation in kobject.c is the source of truth
> (i.e. whether the code needs to be "fixed" to honor the API contract).
>
> > I think that this might be, once again, a false positive. We use kobjects
> > differently than what the kobject implementation and its documentation
> > assume.
>
> I'm curious to hear what Greg says. As Petr pointed out, it seems that the
> documentation for kobjects is inconsistent. If we're going by the function
> comment header in kobject.c then what we have now should probably be
> considered a bug? If we're going by what's in
> Documentation/core-api/kobject.rst, I think what we have now is correct.
I do not understand, what is the problem here? I have been ignoring
this thread :)
> I do think it's a bit of a leaky abstraction to assume that the
> implementation doesn't allocate anything, but I also see Petr's point that
> it could be useful to make it explicit that kobject_init() doesn't allocate
> anything, and instead just affords callers the option of using
> kobject_put() if they want to the objects' destructors to be invoked.
kobject_init() does allocate things internally, where does it say it
does not? What is trying to be "fixed" here?
confused,
greg k-h
next prev parent reply other threads:[~2021-12-14 15:50 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-13 19:17 [PATCH] livepatch: Fix leak on klp_init_patch_early failure path David Vernet
2021-12-13 20:10 ` Josh Poimboeuf
2021-12-13 22:58 ` David Vernet
2021-12-13 23:32 ` Song Liu
2021-12-14 3:13 ` Josh Poimboeuf
2021-12-14 8:45 ` Petr Mladek
2021-12-14 9:17 ` Miroslav Benes
2021-12-14 15:26 ` David Vernet
2021-12-14 15:50 ` Greg Kroah-Hartman [this message]
2021-12-15 8:19 ` Petr Mladek
2021-12-15 15:35 ` Greg Kroah-Hartman
2021-12-16 14:14 ` Petr Mladek
2021-12-16 14:35 ` Greg Kroah-Hartman
2021-12-17 13:10 ` Petr Mladek
2021-12-16 15:14 ` David Vernet
2021-12-17 13:53 ` Petr Mladek
2021-12-15 8:33 ` Miroslav Benes
2021-12-14 15:52 ` Greg Kroah-Hartman
2021-12-14 18:26 ` David Vernet
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