[PATCH 03/10] staging/lustre/llite: Make sure ft_flags is valid

From: Oleg Drokin
Date: Fri Aug 15 2014 - 12:49:51 EST

From: Paul Cassella <cassella@xxxxxxxx>

In ll_fault0, the 'fault' struct is mostly cleared before the call to
cl_io_loop, but ft_flags is not reset. It is ordinarily set by
the call to filemap_fault in vvp_io_kernel_fault, but if Lustre
returns before calling filemap_fault, it still has the old value of

ll_fault0 will then consume the ft_flags field. If it has the
VM_FAULT_RETRY bit set, it will be used as ll_fault0() and
ll_fault()'s return value.

This is a problem when VM_FAULT_RETRY is in ft_flags:
When fault/filemap_fault return with that flag set, they have already
released the mmap semaphore, and do_page_fault does not need to
release it.
Incorrectly returning this flag from ll_fault means mmap_sem
is not upped in the kernel's do_page_fault().

In addition to clearing ft_flags, this patch does not use it unless
it is valid. It's potentially misleading to return ft_flags in
"fault_ret" if ft_flags has not been set by filemap_fault.

This adds clarity, but does not change the current behavior:
When not valid, ft_flags is replaced by fault_ret, which is zero,
as is ft_flags when not set by filemap_fault.

Signed-off-by: Patrick Farrell <paf@xxxxxxxx>
Reviewed-on: http://review.whamcloud.com/10956
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5291
Reviewed-by: Bobi Jam <bobijam@xxxxxxxxx>
Reviewed-by: Jinshan Xiong <jinshan.xiong@xxxxxxxxx>
Signed-off-by: Oleg Drokin <oleg.drokin@xxxxxxxxx>
drivers/staging/lustre/lustre/llite/llite_internal.h | 4 ++++
drivers/staging/lustre/lustre/llite/llite_mmap.c | 8 +++++++-
drivers/staging/lustre/lustre/llite/vvp_io.c | 1 +
3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/lustre/lustre/llite/llite_internal.h b/drivers/staging/lustre/lustre/llite/llite_internal.h
index 634ffa6..684405e 100644
--- a/drivers/staging/lustre/lustre/llite/llite_internal.h
+++ b/drivers/staging/lustre/lustre/llite/llite_internal.h
@@ -894,6 +894,10 @@ struct vvp_io {
* fault API used bitflags for return code.
unsigned int ft_flags;
+ /**
+ * check that flags are from filemap_fault
+ */
+ bool ft_flags_valid;
} fault;
} fault;
} u;
diff --git a/drivers/staging/lustre/lustre/llite/llite_mmap.c b/drivers/staging/lustre/lustre/llite/llite_mmap.c
index 7dae610..5916648 100644
--- a/drivers/staging/lustre/lustre/llite/llite_mmap.c
+++ b/drivers/staging/lustre/lustre/llite/llite_mmap.c
@@ -310,10 +310,16 @@ static int ll_fault0(struct vm_area_struct *vma, struct vm_fault *vmf)
vio->u.fault.ft_vma = vma;
vio->u.fault.ft_vmpage = NULL;
vio->u.fault.fault.ft_vmf = vmf;
+ vio->u.fault.fault.ft_flags = 0;
+ vio->u.fault.fault.ft_flags_valid = 0;

result = cl_io_loop(env, io);

- fault_ret = vio->u.fault.fault.ft_flags;
+ /* ft_flags are only valid if we reached
+ * the call to filemap_fault */
+ if (vio->u.fault.fault.ft_flags_valid)
+ fault_ret = vio->u.fault.fault.ft_flags;
vmpage = vio->u.fault.ft_vmpage;
if (result != 0 && vmpage != NULL) {
diff --git a/drivers/staging/lustre/lustre/llite/vvp_io.c b/drivers/staging/lustre/lustre/llite/vvp_io.c
index a4117d6..fd24874 100644
--- a/drivers/staging/lustre/lustre/llite/vvp_io.c
+++ b/drivers/staging/lustre/lustre/llite/vvp_io.c
@@ -615,6 +615,7 @@ static int vvp_io_kernel_fault(struct vvp_fault_io *cfio)
struct vm_fault *vmf = cfio->fault.ft_vmf;

cfio->fault.ft_flags = filemap_fault(cfio->ft_vma, vmf);
+ cfio->fault.ft_flags_valid = 1;

if (vmf->page) {

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