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Subject[RFC PATCH] doc: fix documentation about UIO_MEM_LOGICAL using
Date
After commit d4fc5069a394 ("mm: switch s_mem and slab_cache in struct page")
page->mapping will be re-used by slab allocations and page->mapping->host
will be used in balance_dirty_pages_ratelimited() as an inode member but
it's not an inode in fact and leads an oops.

[ 159.906493] Unable to handle kernel paging request at virtual address ffff200012d90be8
[ 159.908029] Mem abort info:
[ 159.908552] ESR = 0x96000007
[ 159.909138] Exception class = DABT (current EL), IL = 32 bits
[ 159.910155] SET = 0, FnV = 0
[ 159.910690] EA = 0, S1PTW = 0
[ 159.911241] Data abort info:
[ 159.911846] ISV = 0, ISS = 0x00000007
[ 159.912567] CM = 0, WnR = 0
[ 159.913105] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000042acd000
[ 159.914269] [ffff200012d90be8] pgd=000000043ffff003, pud=000000043fffe003, pmd=000000043fffa003, pte=0000000000000000
[ 159.916280] Internal error: Oops: 96000007 [#1] SMP
[ 159.917195] Dumping ftrace buffer:
[ 159.917845] (ftrace buffer empty)
[ 159.918521] Modules linked in: uio_dev(OE)
[ 159.919276] CPU: 1 PID: 295 Comm: uio_test Tainted: G OE 5.2.0-rc4+ #46
[ 159.920859] Hardware name: linux,dummy-virt (DT)
[ 159.921815] pstate: 60000005 (nZCv daif -PAN -UAO)
[ 159.922809] pc : balance_dirty_pages_ratelimited+0x68/0xc38
[ 159.923965] lr : fault_dirty_shared_page.isra.8+0xe4/0x100
[ 159.925134] sp : ffff800368a77ae0
[ 159.925824] x29: ffff800368a77ae0 x28: 1ffff0006d14ce1a
[ 159.926906] x27: ffff800368a670d0 x26: ffff800368a67120
[ 159.927985] x25: 1ffff0006d10f5fe x24: ffff200012d90be8
[ 159.929089] x23: ffff200013732000 x22: ffff80036ec03200
[ 159.930172] x21: ffff200012d90bc0 x20: 1fffe400025b217d
[ 159.931253] x19: ffff80036ec03200 x18: 0000000000000000
[ 159.932348] x17: 0000000000000000 x16: 0ffffe0000010208
[ 159.933439] x15: 0000000000000000 x14: 0000000000000000
[ 159.934518] x13: 0000000000000000 x12: 0000000000000000
[ 159.935596] x11: 1fffefc001b452c0 x10: ffff0fc001b452c0
[ 159.936697] x9 : dfff200000000000 x8 : dfff200000000001
[ 159.937781] x7 : ffff7e000da29607 x6 : ffff0fc001b452c1
[ 159.938859] x5 : ffff0fc001b452c1 x4 : ffff0fc001b452c1
[ 159.939944] x3 : ffff200010523ad4 x2 : 1fffe400026e659b
[ 159.941065] x1 : dfff200000000000 x0 : ffff200013732cd8
[ 159.942205] Call trace:
[ 159.942732] balance_dirty_pages_ratelimited+0x68/0xc38
[ 159.943797] fault_dirty_shared_page.isra.8+0xe4/0x100
[ 159.944867] do_fault+0x608/0x1250
[ 159.945571] __handle_mm_fault+0x93c/0xfb8
[ 159.946412] handle_mm_fault+0x1c0/0x360
[ 159.947224] do_page_fault+0x358/0x8d0
[ 159.947993] do_translation_fault+0xf8/0x124
[ 159.948884] do_mem_abort+0x70/0x190
[ 159.949624] el0_da+0x24/0x28

According another commit 5e901d0b15c0 ("scsi: qedi: Fix bad pte call trace
when iscsiuio is stopped."), using kmalloc also cause other problem.

But the documentation about UIO_MEM_LOGICAL allows using kmalloc(), remove
and don't allow using kmalloc() in documentation.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
---
Documentation/driver-api/uio-howto.rst | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/driver-api/uio-howto.rst b/Documentation/driver-api/uio-howto.rst
index 25f50ea..8fecfa1 100644
--- a/Documentation/driver-api/uio-howto.rst
+++ b/Documentation/driver-api/uio-howto.rst
@@ -276,8 +276,8 @@ fields of ``struct uio_mem``:
- ``int memtype``: Required if the mapping is used. Set this to
``UIO_MEM_PHYS`` if you you have physical memory on your card to be
mapped. Use ``UIO_MEM_LOGICAL`` for logical memory (e.g. allocated
- with :c:func:`kmalloc()`). There's also ``UIO_MEM_VIRTUAL`` for
- virtual memory.
+ with :c:func:`__get_free_pages()` but not kmalloc()). There's also
+ ``UIO_MEM_VIRTUAL`` for virtual memory.

- ``phys_addr_t addr``: Required if the mapping is used. Fill in the
address of your memory block. This address is the one that appears in
--
1.8.3
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