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Date: Sun, 6 Nov 2016 14:28:02 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Michael Tuexen <tuexen@freebsd.org>
Cc: FreeBSD Current <freebsd-current@freebsd.org>
Subject: Re: New warnings from WITNESS
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On Sun, Nov 06, 2016 at 12:50:12PM +0100, Michael Tuexen wrote:
> bus_dmamap_create with the following non-sleepable locks held:
> exclusive sleep mutex mpt (mpt) r = 0 (0xfffffe0000e2f008) locked @ dev/mpt/mpt.c:2287
> stack backtrace:
> #0 0xffffffff80ac0300 at witness_debugger+0x70
> #1 0xffffffff80ac15e7 at witness_warn+0x3d7
> #2 0xffffffff81055fef at bus_dmamap_create+0x2f
> #3 0xffffffff80678a25 at mpt_configure_ioc+0x3a5
> #4 0xffffffff80677476 at mpt_attach+0x226
> #5 0xffffffff80683299 at mpt_pci_attach+0x9c9
> #6 0xffffffff80a9478d at device_attach+0x41d
> #7 0xffffffff80a9595a at bus_generic_attach+0x4a
> #8 0xffffffff806ebe75 at pci_attach+0xd5
> #9 0xffffffff80a9478d at device_attach+0x41d
> #10 0xffffffff80a9595a at bus_generic_attach+0x4a
> #11 0xffffffff803c11a2 at acpi_pcib_acpi_attach+0x402
> #12 0xffffffff80a9478d at device_attach+0x41d
> #13 0xffffffff80a9595a at bus_generic_attach+0x4a
> #14 0xffffffff803b4c8f at acpi_attach+0xdbf
> #15 0xffffffff80a9478d at device_attach+0x41d
> #16 0xffffffff80a9595a at bus_generic_attach+0x4a
> #17 0xffffffff80ee03e3 at nexus_acpi_attach+0x73
> 
> ... and so on. Not sure which revision introduced it...
r308268

I believe that this is an mpt(4) driver issue, which calls
bus_dmamap_create(9) with the mpt mutex held.