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authorJens Axboe <axboe@kernel.dk>2020-08-10 09:55:22 -0600
committerJens Axboe <axboe@kernel.dk>2020-08-10 15:19:25 -0600
commit7271ef3a93a832180068c7aade3f130b7f39b17e (patch)
tree76050ad8b6c1b5ec953b326e383e898e8273ad5a
parent0ba9c9edcd152158a0e321a4c13ac1dfc571ff3d (diff)
downloadlinux-7271ef3a93a832180068c7aade3f130b7f39b17e.tar.gz
linux-7271ef3a93a832180068c7aade3f130b7f39b17e.tar.xz
io_uring: fix recursive completion locking on oveflow flush
syszbot reports a scenario where we recurse on the completion lock when flushing an overflow: 1 lock held by syz-executor287/6816: #0: ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: io_cqring_overflow_flush+0xc6/0xab0 fs/io_uring.c:1333 stack backtrace: CPU: 1 PID: 6816 Comm: syz-executor287 Not tainted 5.8.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1f0/0x31e lib/dump_stack.c:118 print_deadlock_bug kernel/locking/lockdep.c:2391 [inline] check_deadlock kernel/locking/lockdep.c:2432 [inline] validate_chain+0x69a4/0x88a0 kernel/locking/lockdep.c:3202 __lock_acquire+0x1161/0x2ab0 kernel/locking/lockdep.c:4426 lock_acquire+0x160/0x730 kernel/locking/lockdep.c:5005 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline] _raw_spin_lock_irq+0x67/0x80 kernel/locking/spinlock.c:167 spin_lock_irq include/linux/spinlock.h:379 [inline] io_queue_linked_timeout fs/io_uring.c:5928 [inline] __io_queue_async_work fs/io_uring.c:1192 [inline] __io_queue_deferred+0x36a/0x790 fs/io_uring.c:1237 io_cqring_overflow_flush+0x774/0xab0 fs/io_uring.c:1359 io_ring_ctx_wait_and_kill+0x2a1/0x570 fs/io_uring.c:7808 io_uring_release+0x59/0x70 fs/io_uring.c:7829 __fput+0x34f/0x7b0 fs/file_table.c:281 task_work_run+0x137/0x1c0 kernel/task_work.c:135 exit_task_work include/linux/task_work.h:25 [inline] do_exit+0x5f3/0x1f20 kernel/exit.c:806 do_group_exit+0x161/0x2d0 kernel/exit.c:903 __do_sys_exit_group+0x13/0x20 kernel/exit.c:914 __se_sys_exit_group+0x10/0x10 kernel/exit.c:912 __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Fix this by passing back the link from __io_queue_async_work(), and then let the caller handle the queueing of the link. Take care to also punt the submission reference put to the caller, as we're holding the completion lock for the __io_queue_defer() case. Hence we need to mark the io_kiocb appropriately for that case. Reported-by: syzbot+996f91b6ec3812c48042@syzkaller.appspotmail.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--fs/io_uring.c36
1 files changed, 26 insertions, 10 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c
index af6811ddcfbd..360649041bfa 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -898,6 +898,7 @@ static void io_put_req(struct io_kiocb *req);
static void io_double_put_req(struct io_kiocb *req);
static void __io_double_put_req(struct io_kiocb *req);
static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req);
+static void __io_queue_linked_timeout(struct io_kiocb *req);
static void io_queue_linked_timeout(struct io_kiocb *req);
static int __io_sqe_files_update(struct io_ring_ctx *ctx,
struct io_uring_files_update *ip,
@@ -1179,7 +1180,7 @@ static void io_prep_async_link(struct io_kiocb *req)
io_prep_async_work(cur);
}
-static void __io_queue_async_work(struct io_kiocb *req)
+static struct io_kiocb *__io_queue_async_work(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_kiocb *link = io_prep_linked_timeout(req);
@@ -1187,16 +1188,19 @@ static void __io_queue_async_work(struct io_kiocb *req)
trace_io_uring_queue_async_work(ctx, io_wq_is_hashed(&req->work), req,
&req->work, req->flags);
io_wq_enqueue(ctx->io_wq, &req->work);
-
- if (link)
- io_queue_linked_timeout(link);
+ return link;
}
static void io_queue_async_work(struct io_kiocb *req)
{
+ struct io_kiocb *link;
+
/* init ->work of the whole link before punting */
io_prep_async_link(req);
- __io_queue_async_work(req);
+ link = __io_queue_async_work(req);
+
+ if (link)
+ io_queue_linked_timeout(link);
}
static void io_kill_timeout(struct io_kiocb *req)
@@ -1229,12 +1233,19 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx)
do {
struct io_defer_entry *de = list_first_entry(&ctx->defer_list,
struct io_defer_entry, list);
+ struct io_kiocb *link;
if (req_need_defer(de->req, de->seq))
break;
list_del_init(&de->list);
/* punt-init is done before queueing for defer */
- __io_queue_async_work(de->req);
+ link = __io_queue_async_work(de->req);
+ if (link) {
+ __io_queue_linked_timeout(link);
+ /* drop submission reference */
+ link->flags |= REQ_F_COMP_LOCKED;
+ io_put_req(link);
+ }
kfree(de);
} while (!list_empty(&ctx->defer_list));
}
@@ -5939,15 +5950,12 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
return HRTIMER_NORESTART;
}
-static void io_queue_linked_timeout(struct io_kiocb *req)
+static void __io_queue_linked_timeout(struct io_kiocb *req)
{
- struct io_ring_ctx *ctx = req->ctx;
-
/*
* If the list is now empty, then our linked request finished before
* we got a chance to setup the timer
*/
- spin_lock_irq(&ctx->completion_lock);
if (!list_empty(&req->link_list)) {
struct io_timeout_data *data = &req->io->timeout;
@@ -5955,6 +5963,14 @@ static void io_queue_linked_timeout(struct io_kiocb *req)
hrtimer_start(&data->timer, timespec64_to_ktime(data->ts),
data->mode);
}
+}
+
+static void io_queue_linked_timeout(struct io_kiocb *req)
+{
+ struct io_ring_ctx *ctx = req->ctx;
+
+ spin_lock_irq(&ctx->completion_lock);
+ __io_queue_linked_timeout(req);
spin_unlock_irq(&ctx->completion_lock);
/* drop submission reference */