There is a short window where percpu_refs are already turned zero, but we try to do resurrect(). Play nicer and wait for ->release() to happen in this case and proceed as everything is ok. One downside for ctx refs is that we can ignore signal_pending() on a rare occasion, but someone else should check for it later if needed.

Cc: stable@vger.kernel.org # 5.5+ Signed-off-by: Pavel Begunkov asml.silence@gmail.com --- fs/io_uring.c | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c index b00ab7138410..ce197af2d3c6 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1104,6 +1104,21 @@ static inline void io_set_resource_node(struct io_kiocb *req) } }

+static bool io_refs_resurrect(struct percpu_ref *ref, struct completion *compl) +{ + if (!percpu_ref_tryget(ref)) { + /* already at zero, wait for ->release() */ + if (!try_wait_for_completion(compl)) + synchronize_rcu(); + return false; + } + + percpu_ref_resurrect(ref); + reinit_completion(compl); + percpu_ref_put(ref); + return true; +} + static bool io_match_task(struct io_kiocb *head, struct task_struct *task, struct files_struct *files) @@ -7353,13 +7368,11 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data, flush_delayed_work(&ctx->rsrc_put_work);

ret = wait_for_completion_interruptible(&data->done); - if (!ret) + if (!ret || !io_refs_resurrect(&data->refs, &data->done)) break;

- percpu_ref_resurrect(&data->refs); io_sqe_rsrc_set_node(ctx, data, backup_node); backup_node = NULL; - reinit_completion(&data->done); mutex_unlock(&ctx->uring_lock); ret = io_run_task_work_sig(); mutex_lock(&ctx->uring_lock); @@ -10094,10 +10107,8 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,

mutex_lock(&ctx->uring_lock);

- if (ret) { - percpu_ref_resurrect(&ctx->refs); - goto out_quiesce; - } + if (ret && io_refs_resurrect(&ctx->refs, &ctx->ref_comp)) + return ret; }

if (ctx->restricted) { @@ -10189,7 +10200,6 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode, if (io_register_op_must_quiesce(opcode)) { /* bring the ctx back to life */ percpu_ref_reinit(&ctx->refs); -out_quiesce: reinit_completion(&ctx->ref_comp); } return ret;