[lkml]   [2021]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: dma-api debugfs directory is not created since debugfs is not initialized
On Tue, Apr 27, 2021 at 01:32:50PM +0100, Robin Murphy wrote:
> On 2021-04-27 12:39, Greg KH wrote:
> > On Tue, Apr 27, 2021 at 01:34:27PM +0200, Corentin Labbe wrote:
> > > Hello
> > >
> > > I try to debug some DMA problem on next-20210427, and so I have enabled CONFIG_DMA_API_DEBUG=y.
> > > But the dma-api directory does show up in debugfs, but lot of other directory exists in it.
> >
> > Does it show up properly in 5.12?
> >
> > > After debugging it seems due to commit 56348560d495 ("debugfs: do not attempt to create a new file before the filesystem is initalized")
> > > Reverting the commit permit to "dma-api" debugfs to be found. (but seems not the right way to fix it).
> >
> > We have had some odd start-up ordering issues that the above commit has
> > caused to show. Given that this commit is now in stable kernels, with
> > no report of this issue so far, I'm worried that maybe this is a dma
> > subsystem ordering issue?
> Both debugfs_init() and dma_debug_init() do run at core_initcall level, and
> disassembling the vmlinux from my current working tree does indeed suggest
> that they somehow end up in the wrong relative order:
> [...]
> ffff80001160d0c8 <__initcall__kmod_debug__325_918_dma_debug_init1>:
> ffff80001160d0c8: feb0d528 .word 0xfeb0d528
> [...]
> ffff80001160d108 <__initcall__kmod_debugfs__357_848_debugfs_init1>:
> ffff80001160d108: fff4326c .word 0xfff4326c
> [...]
> I always had the impression that initcall ordering tended to work out
> roughly alphabetical, such that entries from fs/* might come before
> kernel/*, but I guess it's at the whims of the linker in the end :/

init call ordering happens from link ordering.

> Perhaps the easiest thing to do is split out dma_debug_fs_init() and run
> that at a later level? We do want the dma-debug infrastructure itself to be
> up as early as possible, but I think the debugfs view of its internals can
> happily wait until closer to the time that there's actually a userspace to
> be able to look at it.

That seems like a better idea here, there's no need for "special
treatment" of debugfs.


greg k-h

 \ /
  Last update: 2021-04-27 14:42    [W:0.082 / U:0.852 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site