From: Michael Ellerman <mpe@ellerman.id.au>
To: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, robh+dt@kernel.org,
        abdhalee@linux.vnet.ibm.com, paulus@samba.org,
        sachinp@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] powerpc/pseries: fix "OF: ERROR: Bad of_node_put() on /cpus" during DLPAR
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References: <1505473476.9665.13.camel@abdul.in.ibm.com> <1505941372-9147-1-git-send-email-tyreld@linux.vnet.ibm.com>
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Date: Thu, 21 Sep 2017 19:54:51 +1000
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Hi Tyrel,

Thanks for jumping on this.

Tyrel Datwyler <tyreld@linux.vnet.ibm.com> writes:
> Commit 215ee763f8cb ("powerpc: pseries: remove dlpar_attach_node dependency on
> full path") reworked dlpar_attach_node() to no longer look up the parent
> node "/cpus", but instead to have the parent node passed by the caller in the
> function parameter list. As a result dlpar_attach_node() is no longer
> responsible for freeing the reference to the parent node. However,
> commit 215ee763f8cb failed to remove the of_node_put(parent) call in
> dlpar_attach_node(), or to take into account that the reference to the
> parent in the caller dlpar_cpu_add() needs to be held until after
> dlpar_attach_node() returns. As a result doing repeated cpu add/remove dlpar
> operations will eventually result in the following error:
>
> OF: ERROR: Bad of_node_put() on /cpus
> CPU: 0 PID: 10896 Comm: drmgr Not tainted 4.13.0-autotest #1
> Call Trace:
> [c00000026ecdf810] [c00000000278a2a4] dump_stack+0x15c/0x1f8
> (unreliable)
> [c00000026ecdf850] [c0000000025371a4] of_node_release+0x1a4/0x1c0
> [c00000026ecdf8e0] [c0000000027948c8] kobject_put+0x1a8/0x310
> [c00000026ecdf960] [c000000002794bdc] kobject_del+0xbc/0xf0
> [c00000026ecdf990] [c000000002535ff4] __of_detach_node_sysfs+0x144/0x210
> [c00000026ecdf9d0] [c000000002536f70] of_detach_node+0xf0/0x180
> [c00000026ecdfa40] [c0000000016ed494] dlpar_detach_node+0xc4/0x120
> [c00000026ecdfa80] [c0000000016f47d0] dlpar_cpu_remove+0x280/0x560
> [c00000026ecdfb60] [c0000000016f4d9c] dlpar_cpu_release+0xbc/0x1b0
> [c00000026ecdfbb0] [c00000000161279c] arch_cpu_release+0x6c/0xb0
> [c00000026ecdfbe0] [c00000000218ebf0] cpu_release_store+0xa0/0x100
> [c00000026ecdfc20] [c000000002178388] dev_attr_store+0x68/0xa0
> [c00000026ecdfc50] [c000000001bfaae8] sysfs_kf_write+0xa8/0xf0
> [c00000026ecdfc80] [c000000001bf8a3c] kernfs_fop_write+0x2cc/0x400
> [c00000026ecdfce0] [c000000001ad33fc] __vfs_write+0x5c/0x340
> [c00000026ecdfd80] [c000000001ad89e8] vfs_write+0x1a8/0x3d0
> [c00000026ecdfdd0] [c000000001ad9178] SyS_write+0xa8/0x1a0
> [c00000026ecdfe30] [c0000000015eb8e0] system_call+0x58/0x6c

I usually omit all the addresses in the change log, they don't add much
for future readers. I fixed it up myself.

> Fix the issue by removing the of_node_put(parent) call from
> dlpar_attach_node(), and ensuring that the reference to the parent node
> is properly held and released by the caller dlpar_cpu_add().
>
> Fixes: 215ee763f8cb ("powerpc: pseries: remove dlpar_attach_node dependency on full path")
> Cc: stable@vger.kernel.org # v4.13+

It doesn't need to go to stable, v4.13 doesn't have that commit, it's
only in v4.14-rc1.

I dropped the stable tag.

> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> index fc0d8f9..473d817 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> @@ -462,15 +462,17 @@ static ssize_t dlpar_cpu_add(u32 drc_index)
>  	}
>  
>  	dn = dlpar_configure_connector(cpu_to_be32(drc_index), parent);
> -	of_node_put(parent);
>  	if (!dn) {
>  		pr_warn("Failed call to configure-connector, drc index: %x\n",
>  			drc_index);
>  		dlpar_release_drc(drc_index);
> +		of_node_put(parent);
>  		return -EINVAL;
>  	}
>  
>  	rc = dlpar_attach_node(dn, parent);

I added a comment here that I had in my version:

+       /* Regardless we are done with parent now */

> +	of_node_put(parent);
> +
>  	if (rc) {
>  		saved_rc = rc;
>  		pr_warn("Failed to attach node %s, rc: %d, drc index: %x\n",

cheers