On 10/02/2015 04:21 AM, Konstantin Khlebnikov wrote:
Bump. Add more peopple in CC.
On Mon, Sep 21, 2015 at 1:02 PM, Roman Gushchin <kl...@yandex-team.ru> wrote:
I got a report about unkillable task eating CPU. Thge further
investigation shows, that the problem is in the fuse_fill_write_pages()
function. If iov's first segment has zero length, we get an infinite
loop, because we never reach iov_iter_advance() call.
iov_iter_copy_from_user_atomic() eventually calls iterate_iovec(). The
latter silently consumes zero-length iov. So I don't think "iov's first
segment has zero length" can cause infinite loop.
Thanks,
Maxim
Fix this by calling iov_iter_advance() before repeating an attempt to
copy data from userspace.
A similar problem is described in 124d3b7041f ("fix writev regression:
pan hanging unkillable and un-straceable").
Signed-off-by: Roman Gushchin <kl...@yandex-team.ru>
Cc: Miklos Szeredi <mik...@szeredi.hu>
---
fs/fuse/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f523f2f..195476a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1049,6 +1049,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
flush_dcache_page(page);
+ iov_iter_advance(ii, tmp);
if (!tmp) {
unlock_page(page);
page_cache_release(page);
@@ -1061,7 +1062,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
req->page_descs[req->num_pages].length = tmp;
req->num_pages++;
- iov_iter_advance(ii, tmp);
count += tmp;
pos += tmp;
offset += tmp;
--
2.4.3
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