From: Hao Xu haoxu@linux.alibaba.com

commit 8bad28d8a305b0e5ae444c8c3051e8744f5a4296 upstream.

[Backported on top of stable 5.10 since the issue was introduced into it with commit referred in Fixes tag below. The backport is done without `file` to `rsrc` refactoring since it is not in 5.10].

Abaci reported the below issue: [ 141.400455] hrtimer: interrupt took 205853 ns [ 189.869316] process 'usr/local/ilogtail/ilogtail_0.16.26' started with executable stack [ 250.188042] [ 250.188327] ============================================ [ 250.189015] WARNING: possible recursive locking detected [ 250.189732] 5.11.0-rc4 #1 Not tainted [ 250.190267] -------------------------------------------- [ 250.190917] a.out/7363 is trying to acquire lock: [ 250.191506] ffff888114dbcbe8 (&ctx->uring_lock){+.+.}-{3:3}, at: __io_req_task_submit+0x29/0xa0 [ 250.192599] [ 250.192599] but task is already holding lock: [ 250.193309] ffff888114dbfbe8 (&ctx->uring_lock){+.+.}-{3:3}, at: __x64_sys_io_uring_register+0xad/0x210 [ 250.194426] [ 250.194426] other info that might help us debug this: [ 250.195238] Possible unsafe locking scenario: [ 250.195238] [ 250.196019] CPU0 [ 250.196411] ---- [ 250.196803] lock(&ctx->uring_lock); [ 250.197420] lock(&ctx->uring_lock); [ 250.197966] [ 250.197966] *** DEADLOCK *** [ 250.197966] [ 250.198837] May be due to missing lock nesting notation [ 250.198837] [ 250.199780] 1 lock held by a.out/7363: [ 250.200373] #0: ffff888114dbfbe8 (&ctx->uring_lock){+.+.}-{3:3}, at: __x64_sys_io_uring_register+0xad/0x210 [ 250.201645] [ 250.201645] stack backtrace: [ 250.202298] CPU: 0 PID: 7363 Comm: a.out Not tainted 5.11.0-rc4 #1 [ 250.203144] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011 [ 250.203887] Call Trace: [ 250.204302] dump_stack+0xac/0xe3 [ 250.204804] __lock_acquire+0xab6/0x13a0 [ 250.205392] lock_acquire+0x2c3/0x390 [ 250.205928] ? __io_req_task_submit+0x29/0xa0 [ 250.206541] __mutex_lock+0xae/0x9f0 [ 250.207071] ? __io_req_task_submit+0x29/0xa0 [ 250.207745] ? 0xffffffffa0006083 [ 250.208248] ? __io_req_task_submit+0x29/0xa0 [ 250.208845] ? __io_req_task_submit+0x29/0xa0 [ 250.209452] ? __io_req_task_submit+0x5/0xa0 [ 250.210083] __io_req_task_submit+0x29/0xa0 [ 250.210687] io_async_task_func+0x23d/0x4c0 [ 250.211278] task_work_run+0x89/0xd0 [ 250.211884] io_run_task_work_sig+0x50/0xc0 [ 250.212464] io_sqe_files_unregister+0xb2/0x1f0 [ 250.213109] __io_uring_register+0x115a/0x1750 [ 250.213718] ? __x64_sys_io_uring_register+0xad/0x210 [ 250.214395] ? __fget_files+0x15a/0x260 [ 250.214956] __x64_sys_io_uring_register+0xbe/0x210 [ 250.215620] ? trace_hardirqs_on+0x46/0x110 [ 250.216205] do_syscall_64+0x2d/0x40 [ 250.216731] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 250.217455] RIP: 0033:0x7f0fa17e5239 [ 250.218034] Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 3d 01 f0 ff ff 73 01 c3 48 8b 0d 27 ec 2c 00 f7 d8 64 89 01 48 [ 250.220343] RSP: 002b:00007f0fa1eeac48 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab [ 250.221360] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0fa17e5239 [ 250.222272] RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000008 [ 250.223185] RBP: 00007f0fa1eeae20 R08: 0000000000000000 R09: 0000000000000000 [ 250.224091] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 [ 250.224999] R13: 0000000000021000 R14: 0000000000000000 R15: 00007f0fa1eeb700

This is caused by calling io_run_task_work_sig() to do work under uring_lock while the caller io_sqe_files_unregister() already held uring_lock. To fix this issue, briefly drop uring_lock when calling io_run_task_work_sig(), and there are two things to concern:

- hold uring_lock in io_ring_ctx_free() around io_sqe_files_unregister() this is for consistency of lock/unlock. - add new fixed rsrc ref node before dropping uring_lock it's not safe to do io_uring_enter-->percpu_ref_get() with a dying one. - check if rsrc_data->refs is dying to avoid parallel io_sqe_files_unregister

Reported-by: Abaci abaci@linux.alibaba.com Fixes: ce00a7d0d9523 ("io_uring: fix io_sqe_files_unregister() hangs") Suggested-by: Pavel Begunkov asml.silence@gmail.com Signed-off-by: Hao Xu haoxu@linux.alibaba.com [axboe: fixes from Pavel folded in] Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Samiullah Khawaja skhawaja@google.com --- fs/io_uring.c | 82 ++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 61 insertions(+), 21 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c index d1cb1addea96..c5c22b067cd8 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -217,6 +217,7 @@ struct fixed_file_data { struct completion done; struct list_head ref_list; spinlock_t lock; + bool quiesce; };

struct io_buffer { @@ -7105,41 +7106,79 @@ static void io_sqe_files_set_node(struct fixed_file_data *file_data, percpu_ref_get(&file_data->refs); }

-static int io_sqe_files_unregister(struct io_ring_ctx *ctx) -{ - struct fixed_file_data *data = ctx->file_data; - struct fixed_file_ref_node *backup_node, *ref_node = NULL; - unsigned nr_tables, i; - int ret;

- if (!data) - return -ENXIO; - backup_node = alloc_fixed_file_ref_node(ctx); - if (!backup_node) - return -ENOMEM; +static void io_sqe_files_kill_node(struct fixed_file_data *data) +{ + struct fixed_file_ref_node *ref_node = NULL;

spin_lock_bh(&data->lock); ref_node = data->node; spin_unlock_bh(&data->lock); if (ref_node) percpu_ref_kill(&ref_node->refs); +} + +static int io_file_ref_quiesce(struct fixed_file_data *data, + struct io_ring_ctx *ctx) +{ + int ret; + struct fixed_file_ref_node *backup_node;

- percpu_ref_kill(&data->refs); + if (data->quiesce) + return -ENXIO;

- /* wait for all refs nodes to complete */ - flush_delayed_work(&ctx->file_put_work); + data->quiesce = true; do { + backup_node = alloc_fixed_file_ref_node(ctx); + if (!backup_node) + break; + + io_sqe_files_kill_node(data); + percpu_ref_kill(&data->refs); + flush_delayed_work(&ctx->file_put_work); + ret = wait_for_completion_interruptible(&data->done); if (!ret) break; + + percpu_ref_resurrect(&data->refs); + io_sqe_files_set_node(data, backup_node); + backup_node = NULL; + reinit_completion(&data->done); + mutex_unlock(&ctx->uring_lock); ret = io_run_task_work_sig(); - if (ret < 0) { - percpu_ref_resurrect(&data->refs); - reinit_completion(&data->done); - io_sqe_files_set_node(data, backup_node); - return ret; - } + mutex_lock(&ctx->uring_lock); + + if (ret < 0) + break; + backup_node = alloc_fixed_file_ref_node(ctx); + ret = -ENOMEM; + if (!backup_node) + break; } while (1); + data->quiesce = false; + + if (backup_node) + destroy_fixed_file_ref_node(backup_node); + return ret; +} + +static int io_sqe_files_unregister(struct io_ring_ctx *ctx) +{ + struct fixed_file_data *data = ctx->file_data; + unsigned nr_tables, i; + int ret; + + /* + * percpu_ref_is_dying() is to stop parallel files unregister + * Since we possibly drop uring lock later in this function to + * run task work. + */ + if (!data || percpu_ref_is_dying(&data->refs)) + return -ENXIO; + ret = io_file_ref_quiesce(data, ctx); + if (ret) + return ret;

__io_sqe_files_unregister(ctx); nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE); @@ -7150,7 +7189,6 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx) kfree(data); ctx->file_data = NULL; ctx->nr_user_files = 0; - destroy_fixed_file_ref_node(backup_node); return 0; }

@@ -8444,7 +8482,9 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx) css_put(ctx->sqo_blkcg_css); #endif

+ mutex_lock(&ctx->uring_lock); io_sqe_files_unregister(ctx); + mutex_unlock(&ctx->uring_lock); io_eventfd_unregister(ctx); io_destroy_buffers(ctx);