* dma-api debugfs directory is not created since debugfs is not initialized @ 2021-04-27 11:34 Corentin Labbe 2021-04-27 11:39 ` Greg KH 0 siblings, 1 reply; 5+ messages in thread From: Corentin Labbe @ 2021-04-27 11:34 UTC (permalink / raw) To: gregkh, rafael, hch, m.szyprowski, robin.murphy; +Cc: iommu, linux-kernel 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. 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). Regards ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: dma-api debugfs directory is not created since debugfs is not initialized 2021-04-27 11:34 dma-api debugfs directory is not created since debugfs is not initialized Corentin Labbe @ 2021-04-27 11:39 ` Greg KH 2021-04-27 12:32 ` Robin Murphy 2021-04-27 15:36 ` Corentin Labbe 0 siblings, 2 replies; 5+ messages in thread From: Greg KH @ 2021-04-27 11:39 UTC (permalink / raw) To: Corentin Labbe Cc: rafael, hch, m.szyprowski, robin.murphy, iommu, linux-kernel 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? thanks, greg k-h ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: dma-api debugfs directory is not created since debugfs is not initialized 2021-04-27 11:39 ` Greg KH @ 2021-04-27 12:32 ` Robin Murphy 2021-04-27 12:41 ` Greg KH 2021-04-27 15:36 ` Corentin Labbe 1 sibling, 1 reply; 5+ messages in thread From: Robin Murphy @ 2021-04-27 12:32 UTC (permalink / raw) To: Greg KH, Corentin Labbe; +Cc: rafael, hch, m.szyprowski, iommu, linux-kernel 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 :/ 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. Robin. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: dma-api debugfs directory is not created since debugfs is not initialized 2021-04-27 12:32 ` Robin Murphy @ 2021-04-27 12:41 ` Greg KH 0 siblings, 0 replies; 5+ messages in thread From: Greg KH @ 2021-04-27 12:41 UTC (permalink / raw) To: Robin Murphy Cc: Corentin Labbe, rafael, hch, m.szyprowski, iommu, linux-kernel 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 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: dma-api debugfs directory is not created since debugfs is not initialized 2021-04-27 11:39 ` Greg KH 2021-04-27 12:32 ` Robin Murphy @ 2021-04-27 15:36 ` Corentin Labbe 1 sibling, 0 replies; 5+ messages in thread From: Corentin Labbe @ 2021-04-27 15:36 UTC (permalink / raw) To: Greg KH; +Cc: rafael, hch, m.szyprowski, robin.murphy, iommu, linux-kernel Le Tue, Apr 27, 2021 at 01:39:16PM +0200, Greg KH a écrit : > 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? > No (Tested on a qemu x86_64) ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-04-27 15:36 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-04-27 11:34 dma-api debugfs directory is not created since debugfs is not initialized Corentin Labbe 2021-04-27 11:39 ` Greg KH 2021-04-27 12:32 ` Robin Murphy 2021-04-27 12:41 ` Greg KH 2021-04-27 15:36 ` Corentin Labbe
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