linux-kernel - [PATCH] infiniband: add MMU dependency for user

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Date:   Fri,  6 Oct 2017 09:13:46 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Doug Ledford <dledford@...hat.com>,
        Sean Hefty <sean.hefty@...el.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Yuval Shaia <yuval.shaia@...cle.com>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] infiniband: add MMU dependency for user_mem

The infiniband subsystem causes a link failure when the umem
driver is built on MMU-less systems:

mm/mmu_notifier.o: In function `do_mmu_notifier_register':
mmu_notifier.c:(.text+0x32): undefined reference to `mm_take_all_locks'
drivers/infiniband/core/umem.o: In function `ib_umem_get':
umem.c:(.text+0x132): undefined reference to `can_do_mlock'
drivers/infiniband/core/umem_odp.o: In function `ib_umem_odp_map_dma_pages':
umem_odp.c:(.text+0x766): undefined reference to `get_user_pages_remote'

This bug has existed for a while but only become apparent in ARM
randconfig builds when the dependency on PCI was lifted, as none
of the ARM-NOMMU targets support PCI at the moment.

We could probably get the umem driver to build by providing an
alternative implementation 'can_do_mlock()' that returns false
on NOMMU-systems, but then we'd still have a problem with the
mmu-notifiers required by CONFIG_INFINIBAND_ON_DEMAND_PAGING,
so simply forbidding umem with NOMMU seems like the simplest
workaround.

Fixes: 931bc0d91639 ("IB: Move PCI dependency from root KConfig to HW's KConfigs")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/infiniband/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/infiniband/Kconfig b/drivers/infiniband/Kconfig
index b62b3b1e09cd..98ac46ed7214 100644
--- a/drivers/infiniband/Kconfig
+++ b/drivers/infiniband/Kconfig
@@ -45,6 +45,7 @@ config INFINIBAND_EXP_USER_ACCESS
 config INFINIBAND_USER_MEM
 	bool
 	depends on INFINIBAND_USER_ACCESS != n
+	depends on MMU
 	default y
 
 config INFINIBAND_ON_DEMAND_PAGING
-- 
2.9.0