Re: [PATCH] kernfs: fix memleak in kernel_ops_readdir()

[Greg Kroah-Hartman]

On Wed, Aug 07, 2019 at 11:45:18AM -0700, Tejun Heo wrote:
> Hello,
> 
> On Wed, Aug 07, 2019 at 06:29:28AM -0700, Tony Lindgren wrote:
> > Hi,
> > 
> > * Tejun Heo <tj@xxxxxxxxxx> [691231 23:00]:
> > > From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > > 
> > > If getdents64 is killed or hits on segfault, it'll leave cgroups
> > > directories in sysfs pinned leaking memory because the kernfs node
> > > won't be freed on rmdir and the parent neither.
> > 
> > Somehow this causes a regression in Linux next for me where I'm seeing
> > lots of sysfs entries now missing under /sys/bus/platform/devices.
> > 
> > For example, I now only see one .serial entry show up in sysfs.
> > Things work again if I revert commit cc798c83898e ("kernfs: fix memleak
> > inkernel_ops_readdir()"). Any ideas why that would be?
> > 
> > Below is a diff -u of ls /sys/bus/platform/devices for reference
> > showing the missing entries with cc798c83898e.
> 
> Ugh, you're right.  It can get double-put cuz ctx->pos is put by
> release too.  Greg, sorry about the noise but can you please revert
> the patch?  I'll look into why this looked like memory leak from
> slabinfo side.

Now reverted, thanks.

greg k-h