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SubjectRe: WARNING in csum_and_copy_to_iter
On Sat, Nov 24, 2018 at 09:44:36PM +0000, Al Viro wrote:

> No point, IMO - the fix isn't hard and bisect hazard created by the whole thing
> is both mild (spurious WARN() in case that used to fail anyway) _and_ won't
> disappear from reverting, obviously. I'll post a fix later tonight...

FWIW, I think the following ought to work; it's obviously a pair of commits
(introduction of convenience helper/switch to its use + csum_and_copy_to_iter()
for ITER_PIPE), as well as commit message, etc., but I would really appreciate
if folks gave it a look _and_ a beating.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 7ebccb5c1637..621984743268 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -560,6 +560,44 @@ static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
return bytes;
}

+static __wsum csum_and_memcpy(void *to, const void *from, size_t len,
+ __wsum sum, size_t off)
+{
+ __wsum next = csum_partial_copy_nocheck(from, to, len, 0);
+ return csum_block_add(sum, next, off);
+}
+
+static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
+ __wsum *csum, struct iov_iter *i)
+{
+ struct pipe_inode_info *pipe = i->pipe;
+ size_t n, r;
+ size_t off = 0;
+ __wsum sum = *csum;
+ int idx;
+
+ if (!sanity(i))
+ return 0;
+
+ bytes = n = push_pipe(i, bytes, &idx, &r);
+ if (unlikely(!n))
+ return 0;
+ for ( ; n; idx = next_idx(idx, pipe), r = 0) {
+ size_t chunk = min_t(size_t, n, PAGE_SIZE - r);
+ char *p = kmap_atomic(pipe->bufs[idx].page);
+ sum = csum_and_memcpy(p + r, addr, chunk, sum, off);
+ kunmap_atomic(p);
+ i->idx = idx;
+ i->iov_offset = r + chunk;
+ n -= chunk;
+ off += chunk;
+ addr += chunk;
+ }
+ i->count -= bytes;
+ *csum = sum;
+ return bytes;
+}
+
size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
{
const char *from = addr;
@@ -1368,17 +1406,15 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
err ? v.iov_len : 0;
}), ({
char *p = kmap_atomic(v.bv_page);
- next = csum_partial_copy_nocheck(p + v.bv_offset,
- (to += v.bv_len) - v.bv_len,
- v.bv_len, 0);
+ sum = csum_and_memcpy((to += v.bv_len) - v.bv_len,
+ p + v.bv_offset, v.bv_len,
+ sum, off);
kunmap_atomic(p);
- sum = csum_block_add(sum, next, off);
off += v.bv_len;
}),({
- next = csum_partial_copy_nocheck(v.iov_base,
- (to += v.iov_len) - v.iov_len,
- v.iov_len, 0);
- sum = csum_block_add(sum, next, off);
+ sum = csum_and_memcpy((to += v.iov_len) - v.iov_len,
+ v.iov_base, v.iov_len,
+ sum, off);
off += v.iov_len;
})
)
@@ -1412,17 +1448,15 @@ bool csum_and_copy_from_iter_full(void *addr, size_t bytes, __wsum *csum,
0;
}), ({
char *p = kmap_atomic(v.bv_page);
- next = csum_partial_copy_nocheck(p + v.bv_offset,
- (to += v.bv_len) - v.bv_len,
- v.bv_len, 0);
+ sum = csum_and_memcpy((to += v.bv_len) - v.bv_len,
+ p + v.bv_offset, v.bv_len,
+ sum, off);
kunmap_atomic(p);
- sum = csum_block_add(sum, next, off);
off += v.bv_len;
}),({
- next = csum_partial_copy_nocheck(v.iov_base,
- (to += v.iov_len) - v.iov_len,
- v.iov_len, 0);
- sum = csum_block_add(sum, next, off);
+ sum = csum_and_memcpy((to += v.iov_len) - v.iov_len,
+ v.iov_base, v.iov_len,
+ sum, off);
off += v.iov_len;
})
)
@@ -1438,8 +1472,12 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, __wsum *csum,
const char *from = addr;
__wsum sum, next;
size_t off = 0;
+
+ if (unlikely(iov_iter_is_pipe(i)))
+ return csum_and_copy_to_pipe_iter(addr, bytes, csum, i);
+
sum = *csum;
- if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
+ if (unlikely(iov_iter_is_discard(i))) {
WARN_ON(1); /* for now */
return 0;
}
@@ -1455,17 +1493,15 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, __wsum *csum,
err ? v.iov_len : 0;
}), ({
char *p = kmap_atomic(v.bv_page);
- next = csum_partial_copy_nocheck((from += v.bv_len) - v.bv_len,
- p + v.bv_offset,
- v.bv_len, 0);
+ sum = csum_and_memcpy(p + v.bv_offset,
+ (from += v.bv_len) - v.bv_len,
+ v.bv_len, sum, off);
kunmap_atomic(p);
- sum = csum_block_add(sum, next, off);
off += v.bv_len;
}),({
- next = csum_partial_copy_nocheck((from += v.iov_len) - v.iov_len,
- v.iov_base,
- v.iov_len, 0);
- sum = csum_block_add(sum, next, off);
+ sum = csum_and_memcpy(v.iov_base,
+ (from += v.iov_len) - v.iov_len,
+ v.iov_len, sum, off);
off += v.iov_len;
})
)
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