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Date:   Sat, 14 May 2022 22:56:04 +0300
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From:   Vasily Averin <vvs@openvz.org>
Subject: [PATCH v2] sparse: use force attribute for vm_fault_t casts
To:     Dan Williams <dan.j.williams@intel.com>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Cc:     kernel@openvz.org, linux-kernel@vger.kernel.org,
        nvdimm@lists.linux.dev, linux-fsdevel@vger.kernel.org
References: <Yn/oKz6v5GkReeA3@casper.infradead.org>
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Fixes sparse warnings:
./include/trace/events/fs_dax.h:10:1: sparse:
    got restricted vm_fault_t
./include/trace/events/fs_dax.h:153:1: sparse:
    got restricted vm_fault_t
fs/dax.c:563:39: sparse:    got restricted vm_fault_t
fs/dax.c:565:39: sparse:    got restricted vm_fault_t
fs/dax.c:569:31: sparse:    got restricted vm_fault_t
fs/dax.c:1055:41: sparse:
    got restricted vm_fault_t [assigned] [usertype] ret
fs/dax.c:1461:46: sparse:    got restricted vm_fault_t [usertype] ret
fs/dax.c:1477:21: sparse:
    expected restricted vm_fault_t [assigned] [usertype] ret
fs/dax.c:1518:51: sparse:
    got restricted vm_fault_t [assigned] [usertype] ret
fs/dax.c:1599:21: sparse:
    expected restricted vm_fault_t [assigned] [usertype] ret
fs/dax.c:1633:62: sparse:
    got restricted vm_fault_t [assigned] [usertype] ret
fs/dax.c:1696:55: sparse:    got restricted vm_fault_t
fs/dax.c:1711:58: sparse:
    got restricted vm_fault_t [assigned] [usertype] ret

vm_fault_t type is bitwise and requires __force attribute for any casts.

Signed-off-by: Vasily Averin <vvs@openvz.org>
---
v2: improved according to the recommendations of Matthew Wilcox:
   - __force cast moved into internal functions
   - introduced new abstractions dax_vm_fault_[en|de]code()
---
 fs/dax.c                      | 21 +++++++++++++++------
 include/linux/mm_types.h      | 30 ++++++++++++++++--------------
 include/trace/events/fs_dax.h | 12 ++++++------
 3 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 67a08a32fccb..c27c8782007f 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -121,6 +121,15 @@ static int dax_is_empty_entry(void *entry)
 	return xa_to_value(entry) & DAX_EMPTY;
 }
 
+static void *dax_vm_fault_encode(vm_fault_t fault)
+{
+	return xa_mk_internal((__force unsigned long)fault);
+}
+
+static vm_fault_t dax_vm_fault_decode(void *entry)
+{
+	return (__force vm_fault_t)xa_to_internal(entry);
+}
 /*
  * true if the entry that was found is of a smaller order than the entry
  * we were looking for
@@ -560,13 +569,13 @@ static void *grab_mapping_entry(struct xa_state *xas,
 	if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
 		goto retry;
 	if (xas->xa_node == XA_ERROR(-ENOMEM))
-		return xa_mk_internal(VM_FAULT_OOM);
+		return dax_vm_fault_encode(VM_FAULT_OOM);
 	if (xas_error(xas))
-		return xa_mk_internal(VM_FAULT_SIGBUS);
+		return dax_vm_fault_encode(VM_FAULT_SIGBUS);
 	return entry;
 fallback:
 	xas_unlock_irq(xas);
-	return xa_mk_internal(VM_FAULT_FALLBACK);
+	return dax_vm_fault_encode(VM_FAULT_FALLBACK);
 }
 
 /**
@@ -1474,7 +1483,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 
 	entry = grab_mapping_entry(&xas, mapping, 0);
 	if (xa_is_internal(entry)) {
-		ret = xa_to_internal(entry);
+		ret = dax_vm_fault_decode(entry);
 		goto out;
 	}
 
@@ -1578,7 +1587,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	 */
 	max_pgoff = DIV_ROUND_UP(i_size_read(iter.inode), PAGE_SIZE);
 
-	trace_dax_pmd_fault(iter.inode, vmf, max_pgoff, 0);
+	trace_dax_pmd_fault(iter.inode, vmf, max_pgoff, (vm_fault_t)0);
 
 	if (xas.xa_index >= max_pgoff) {
 		ret = VM_FAULT_SIGBUS;
@@ -1596,7 +1605,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	 */
 	entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
 	if (xa_is_internal(entry)) {
-		ret = xa_to_internal(entry);
+		ret = dax_vm_fault_decode(entry);
 		goto fallback;
 	}
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 8834e38c06a4..57cc4918b1b1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -745,20 +745,22 @@ enum vm_fault_reason {
 			VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON |	\
 			VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)
 
-#define VM_FAULT_RESULT_TRACE \
-	{ VM_FAULT_OOM,                 "OOM" },	\
-	{ VM_FAULT_SIGBUS,              "SIGBUS" },	\
-	{ VM_FAULT_MAJOR,               "MAJOR" },	\
-	{ VM_FAULT_WRITE,               "WRITE" },	\
-	{ VM_FAULT_HWPOISON,            "HWPOISON" },	\
-	{ VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" },	\
-	{ VM_FAULT_SIGSEGV,             "SIGSEGV" },	\
-	{ VM_FAULT_NOPAGE,              "NOPAGE" },	\
-	{ VM_FAULT_LOCKED,              "LOCKED" },	\
-	{ VM_FAULT_RETRY,               "RETRY" },	\
-	{ VM_FAULT_FALLBACK,            "FALLBACK" },	\
-	{ VM_FAULT_DONE_COW,            "DONE_COW" },	\
-	{ VM_FAULT_NEEDDSYNC,           "NEEDDSYNC" }
+#define faultflag_string(flag) {(__force unsigned long)VM_FAULT_##flag, #flag}
+
+#define VM_FAULT_RESULT_TRACE			\
+	faultflag_string(OOM),			\
+	faultflag_string(SIGBUS),		\
+	faultflag_string(MAJOR),		\
+	faultflag_string(WRITE),		\
+	faultflag_string(HWPOISON),		\
+	faultflag_string(HWPOISON_LARGE),	\
+	faultflag_string(SIGSEGV),		\
+	faultflag_string(NOPAGE),		\
+	faultflag_string(LOCKED),		\
+	faultflag_string(RETRY),		\
+	faultflag_string(FALLBACK),		\
+	faultflag_string(DONE_COW),		\
+	faultflag_string(NEEDDSYNC)
 
 struct vm_special_mapping {
 	const char *name;	/* The name, e.g. "[vdso]". */
diff --git a/include/trace/events/fs_dax.h b/include/trace/events/fs_dax.h
index 97b09fcf7e52..75908bdc7b2d 100644
--- a/include/trace/events/fs_dax.h
+++ b/include/trace/events/fs_dax.h
@@ -9,7 +9,7 @@
 
 DECLARE_EVENT_CLASS(dax_pmd_fault_class,
 	TP_PROTO(struct inode *inode, struct vm_fault *vmf,
-		pgoff_t max_pgoff, int result),
+		pgoff_t max_pgoff, vm_fault_t result),
 	TP_ARGS(inode, vmf, max_pgoff, result),
 	TP_STRUCT__entry(
 		__field(unsigned long, ino)
@@ -33,7 +33,7 @@ DECLARE_EVENT_CLASS(dax_pmd_fault_class,
 		__entry->flags = vmf->flags;
 		__entry->pgoff = vmf->pgoff;
 		__entry->max_pgoff = max_pgoff;
-		__entry->result = result;
+		__entry->result = (__force int)result;
 	),
 	TP_printk("dev %d:%d ino %#lx %s %s address %#lx vm_start "
 			"%#lx vm_end %#lx pgoff %#lx max_pgoff %#lx %s",
@@ -54,7 +54,7 @@ DECLARE_EVENT_CLASS(dax_pmd_fault_class,
 #define DEFINE_PMD_FAULT_EVENT(name) \
 DEFINE_EVENT(dax_pmd_fault_class, name, \
 	TP_PROTO(struct inode *inode, struct vm_fault *vmf, \
-		pgoff_t max_pgoff, int result), \
+		pgoff_t max_pgoff, vm_fault_t result), \
 	TP_ARGS(inode, vmf, max_pgoff, result))
 
 DEFINE_PMD_FAULT_EVENT(dax_pmd_fault);
@@ -151,7 +151,7 @@ DEFINE_EVENT(dax_pmd_insert_mapping_class, name, \
 DEFINE_PMD_INSERT_MAPPING_EVENT(dax_pmd_insert_mapping);
 
 DECLARE_EVENT_CLASS(dax_pte_fault_class,
-	TP_PROTO(struct inode *inode, struct vm_fault *vmf, int result),
+	TP_PROTO(struct inode *inode, struct vm_fault *vmf, vm_fault_t result),
 	TP_ARGS(inode, vmf, result),
 	TP_STRUCT__entry(
 		__field(unsigned long, ino)
@@ -169,7 +169,7 @@ DECLARE_EVENT_CLASS(dax_pte_fault_class,
 		__entry->address = vmf->address;
 		__entry->flags = vmf->flags;
 		__entry->pgoff = vmf->pgoff;
-		__entry->result = result;
+		__entry->result = (__force int)result;
 	),
 	TP_printk("dev %d:%d ino %#lx %s %s address %#lx pgoff %#lx %s",
 		MAJOR(__entry->dev),
@@ -185,7 +185,7 @@ DECLARE_EVENT_CLASS(dax_pte_fault_class,
 
 #define DEFINE_PTE_FAULT_EVENT(name) \
 DEFINE_EVENT(dax_pte_fault_class, name, \
-	TP_PROTO(struct inode *inode, struct vm_fault *vmf, int result), \
+	TP_PROTO(struct inode *inode, struct vm_fault *vmf, vm_fault_t result), \
 	TP_ARGS(inode, vmf, result))
 
 DEFINE_PTE_FAULT_EVENT(dax_pte_fault);
-- 
2.31.1