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Subject[PATCH 5.9 054/152] io_uring: handle -EOPNOTSUPP on path resolution
Date
From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 944d1444d53f5a213457e5096db370cfd06923d4 ]

Any attempt to do path resolution on /proc/self from an async worker will
yield -EOPNOTSUPP. We can safely do that resolution from the task itself,
and without blocking, so retry it from there.

Ideally io_uring would know this upfront and not have to go through the
worker thread to find out, but that doesn't currently seem feasible.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 185c206e5683f..5d9f8e40b93d3 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -436,6 +436,7 @@ struct io_sr_msg {
struct io_open {
struct file *file;
int dfd;
+ bool ignore_nonblock;
struct filename *filename;
struct open_how how;
unsigned long nofile;
@@ -3591,6 +3592,7 @@ static int __io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
return ret;
}
req->open.nofile = rlimit(RLIMIT_NOFILE);
+ req->open.ignore_nonblock = false;
req->flags |= REQ_F_NEED_CLEANUP;
return 0;
}
@@ -3638,7 +3640,7 @@ static int io_openat2(struct io_kiocb *req, bool force_nonblock)
struct file *file;
int ret;

- if (force_nonblock)
+ if (force_nonblock && !req->open.ignore_nonblock)
return -EAGAIN;

ret = build_open_flags(&req->open.how, &op);
@@ -3653,6 +3655,21 @@ static int io_openat2(struct io_kiocb *req, bool force_nonblock)
if (IS_ERR(file)) {
put_unused_fd(ret);
ret = PTR_ERR(file);
+ /*
+ * A work-around to ensure that /proc/self works that way
+ * that it should - if we get -EOPNOTSUPP back, then assume
+ * that proc_self_get_link() failed us because we're in async
+ * context. We should be safe to retry this from the task
+ * itself with force_nonblock == false set, as it should not
+ * block on lookup. Would be nice to know this upfront and
+ * avoid the async dance, but doesn't seem feasible.
+ */
+ if (ret == -EOPNOTSUPP && io_wq_current_is_worker()) {
+ req->open.ignore_nonblock = true;
+ refcount_inc(&req->refs);
+ io_req_task_queue(req);
+ return 0;
+ }
} else {
fsnotify_open(file);
fd_install(ret, file);
--
2.27.0


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