Re: [1/2] powerpc/pseries: fix "OF: ERROR: Bad of_node_put() on /cpus" during DLPAR

[Abdul Haleem]

On Fri, 2017-09-22 at 11:03 +1000, Michael Ellerman wrote:
> On Wed, 2017-09-20 at 21:02:51 UTC, Tyrel Datwyler wrote:
> > 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
> > 
> > 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().
> > 
> > Cc: stable@xxxxxxxxxxxxxxx # v4.13+
> > Fixes: 215ee763f8cb ("powerpc: pseries: remove dlpar_attach_node dependency on full path")
> > Signed-off-by: Tyrel Datwyler <tyreld@xxxxxxxxxxxxxxxxxx>
> > Reported-by: Abdul Haleem <abdhalee@xxxxxxxxxxxxxxxxxx>
> 
> Series applied to powerpc fixes, thanks.
> 
> https://git.kernel.org/powerpc/c/087ff6a5ae3052bb2835e191094b79

The patch fixes the problem, No warnings seen for 100 iterations of
DLPAR CPU add/remove operation.

Thanks Tyrel and Michael.

Tested-by: Abdul Haleem <abdhalee@xxxxxxxxxxxxxxxxxx>

-- 
Regard's

Abdul Haleem
IBM Linux Technology Centre