> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxx>
> Sent: Thursday, March 26, 2020 1:26 PM
> To: Dalessandro, Dennis <dennis.dalessandro@xxxxxxxxx>
> Cc: dledford@xxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx; Marciniszyn, Mike
> <mike.marciniszyn@xxxxxxxxx>; stable@xxxxxxxxxxxxxxx; Wan, Kaike
> <kaike.wan@xxxxxxxxx>
> Subject: Re: [PATCH for-rc 1/2] IB/hfi1: Fix memory leaks in sysfs registration
> and unregistration
>
> On Thu, Mar 26, 2020 at 12:38:07PM -0400, Dennis Dalessandro wrote:
> > From: Kaike Wan <kaike.wan@xxxxxxxxx>
> >
> > When the hfi1 driver is unloaded, kmemleak will report the following
> > issue:
> >
> > unreferenced object 0xffff8888461a4c08 (size 8):
> > comm "kworker/0:0", pid 5, jiffies 4298601264 (age 2047.134s) hex dump
> > (first 8 bytes):
> > 73 64 6d 61 30 00 ff ff sdma0...
> > backtrace:
> > [<00000000311a6ef5>] kvasprintf+0x62/0xd0 [<00000000ade94d9f>]
> > kobject_set_name_vargs+0x1c/0x90 [<0000000060657dbb>]
> > kobject_init_and_add+0x5d/0xb0 [<00000000346fe72b>] 0xffffffffa0c5ecba
> > [<000000006cfc5819>] 0xffffffffa0c866b9 [<0000000031c65580>]
> > 0xffffffffa0c38e87 [<00000000e9739b3f>] local_pci_probe+0x41/0x80
> > [<000000006c69911d>] work_for_cpu_fn+0x16/0x20
> [<00000000601267b5>]
> > process_one_work+0x171/0x380 [<0000000049a0eefa>]
> > worker_thread+0x1d1/0x3f0 [<00000000909cf2b9>] kthread+0xf8/0x130
> > [<0000000058f5f874>] ret_from_fork+0x35/0x40
> >
> > This patch fixes the issue by:
> > - Releasing dd->per_sdma[i].kobject in hfi1_unregister_sysfs().
> > - This will fix the memory leak.
> > - Calling kobject_put() to unwind operations only for those entries in
> > dd->per_sdma[] whose operations have succeeded (including the current
> > one that has just failed) in hfi1_verbs_register_sysfs().
> >
> > Fixes: 0cb2aa690c7e ("IB/hfi1: Add sysfs interface for affinity
> > setup")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Reviewed-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
> > Signed-off-by: Kaike Wan <kaike.wan@xxxxxxxxx>
> > Signed-off-by: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
> > ---
> > drivers/infiniband/hw/hfi1/sysfs.c | 13 +++++++++++--
> > 1 file changed, 11 insertions(+), 2 deletions(-)
>
> I'm not certain, but this seems unwise.
>
> After hfi1_verbs_unregiser_sysfs() returns there should be no sysfs left
> under the ibdev as we are going to delete the ibdev sysfs next.
>
> kobject_del() triggers synchronous delete of the sysfs, while
> kobject_put() potentially defers it to the future.
True. However, kobject_del() will only delete the sysfs for the object, ie, unwrap what has been done in object_add, but it will not decrement the refcount for the kobject.
To unwap kobject_init_and_add(), one can call
(1) kobject_del() (optional)
(2) object_put()
The kobject cleanup function (kobject_cleanup()) will call kobject_del if kobj->state_in_sys is set. Therefore, one can call object_put() alone to get the job done.
>
> Will ib unregister fail if the kobject_del() has not happened yet? I am unsure.
>
I don't think so. We only observed the kmemleak complaints after unloading the driver, nothing else.
Kaike
