[RFC PATCH 04/13] fs/userfaultfd: simplify locks in userfaultfd_ctx_read

Nadav Amit
2020-11-29T00:50:38Z

Small refactoring to reduce the number of locations in which locks are
released in userfaultfd_ctx_read(), as this makes the understanding of
the code and its changes harder.

No functional change intended.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Signed-off-by: Nadav Amit <namit@vmware.com>
---
fs/userfaultfd.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 4fe07c1a44c6..fedf7c1615d5 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1039,6 +1039,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
set_current_state(TASK_INTERRUPTIBLE);
spin_lock(&ctx->fault_pending_wqh.lock);
uwq = find_userfault(ctx);
+ ret = -EAGAIN;
if (uwq) {
/*
* Use a seqcount to repeat the lockless check
@@ -1077,11 +1078,11 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,

/* careful to always initialize msg if ret == 0 */
*msg = uwq->msg;
- spin_unlock(&ctx->fault_pending_wqh.lock);
ret = 0;
- break;
}
spin_unlock(&ctx->fault_pending_wqh.lock);
+ if (!ret)
+ break;

spin_lock(&ctx->event_wqh.lock);
uwq = find_userfault_evt(ctx);
@@ -1099,17 +1100,14 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
* reference on it.
*/
userfaultfd_ctx_get(fork_nctx);
- spin_unlock(&ctx->event_wqh.lock);
- ret = 0;
- break;
+ } else {
+ userfaultfd_event_complete(ctx, uwq);
}
-
- userfaultfd_event_complete(ctx, uwq);
- spin_unlock(&ctx->event_wqh.lock);
ret = 0;
- break;
}
spin_unlock(&ctx->event_wqh.lock);
+ if (!ret)
+ break;

if (signal_pending(current)) {
ret = -ERESTARTSYS;
--
2.25.1