linux-kernel - Re: [PATCH v2] ARM: OMAP2+: Fix device node reference counts

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Message-ID: <20170301232948.GJ20572@atomide.com>
Date:   Wed, 1 Mar 2017 15:29:48 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Paul Walmsley <paul@...an.com>,
        Russell King <linux@...linux.org.uk>,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Qi Hou <qi.hou@...driver.com>,
        Peter Rosin <peda@...ntia.se>, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2] ARM: OMAP2+: Fix device node reference counts

* Guenter Roeck <linux@...ck-us.net> [170301 12:16]:
> On Wed, Mar 01, 2017 at 10:04:39AM -0800, Tony Lindgren wrote:
> > * Guenter Roeck <linux@...ck-us.net> [170228 11:55]:
> > > After commit 'of: fix of_node leak caused in of_find_node_opts_by_path',
> > > the following error may be reported when running omap images.
> > > 
> > > OF: ERROR: Bad of_node_put() on /ocp@...00000
> > > CPU: 0 PID: 0 Comm: swapper Not tainted 4.10.0-rc7-next-20170210 #1
> > > Hardware name: Generic OMAP3-GP (Flattened Device Tree)
> > > [<c0310604>] (unwind_backtrace) from [<c030bbf4>] (show_stack+0x10/0x14)
> > > [<c030bbf4>] (show_stack) from [<c05add8c>] (dump_stack+0x98/0xac)
> > > [<c05add8c>] (dump_stack) from [<c05af1b0>] (kobject_release+0x48/0x7c)
> > > [<c05af1b0>] (kobject_release)
> > > 	from [<c0ad1aa4>] (of_find_node_by_name+0x74/0x94)
> > > [<c0ad1aa4>] (of_find_node_by_name)
> > > 	from [<c1215bd4>] (omap3xxx_hwmod_is_hs_ip_block_usable+0x24/0x2c)
> > > [<c1215bd4>] (omap3xxx_hwmod_is_hs_ip_block_usable) from
> > > [<c1215d5c>] (omap3xxx_hwmod_init+0x180/0x274)
> > > [<c1215d5c>] (omap3xxx_hwmod_init)
> > > 	from [<c120faa8>] (omap3_init_early+0xa0/0x11c)
> > > [<c120faa8>] (omap3_init_early)
> > > 	from [<c120fb2c>] (omap3430_init_early+0x8/0x30)
> > > [<c120fb2c>] (omap3430_init_early)
> > > 	from [<c1204710>] (setup_arch+0xc04/0xc34)
> > > [<c1204710>] (setup_arch) from [<c1200948>] (start_kernel+0x68/0x38c)
> > > [<c1200948>] (start_kernel) from [<8020807c>] (0x8020807c)
> > > 
> > > of_find_node_by_name() drops the reference to the passed device node.
> > > Use of_get_child_by_name() instead. Also, release references to
> > > device nodes obtained with of_find_node_by_name() and
> > > of_get_child_by_name() after they are no longer needed.
> > > 
> > > While at it, clean up the code and change the return type of
> > > omap3xxx_hwmod_is_hs_ip_block_usable() to bool to match its use
> > > and the return type of of_device_is_available().
> > > 
> > > Cc: Qi Hou <qi.hou@...driver.com>
> > > Cc: Peter Rosin <peda@...ntia.se>
> > > Cc: Rob Herring <robh@...nel.org>
> > > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > > ---
> > > v2: Change subject ('Grab reference to device nodes where needed'
> > >     didn't really cover all the changes made)
> > >     Use of_get_child_by_name() instead of of_find_node_by_name()
> > >     Drop references to device nodes as needed
> > >     Change return type of omap3xxx_hwmod_is_hs_ip_block_usable()
> > >     to bool
> > 
> > OK so now we have a commit id for it and should have:
> > 
> > Fixes: 0549bde0fcb1 ("of: fix of_node leak caused in
> > of_find_node_opts_by_path")
> > 
> Not really; 0549bde0fcb1 fixes a bug and hides _this_ bug.
> More appropriate, if that would exist, would be something like
> 
> Exposed-by: 0549bde0fcb1 ("of: fix of_node leak caused in ...")

OK

> > What about other leaky users of of_find_node_by_name() and
> > of_get_child_by_name()?
> > 
> > We have those in:
> > 
> > control.c
> > display.c
> > omap_device.c
> > omap_hwmod.c
> > 
> 
> I am sure there are many more. For example, the bug solved in my patch
> "disappears" if one adds some delays (or just log messages) at strategic
> areas in the code. Such delays result in node leaks elsewhere, which
> again hides the bug I am trying to fix with my patch.
> 
> > So probably it really should be two fixes, one for the regression
> > causing the error. Then another one for fixing the leaky np use.
> > 
> No problem; I 'll split into two patches.

OK thanks.

Tony