Messages in this thread | | | Date | Tue, 27 Apr 2021 14:41:15 +0200 | From | Greg KH <> | Subject | Re: dma-api debugfs directory is not created since debugfs is not initialized |
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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.
thanks,
greg k-h
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