There is a fancy bug, where exiting user task may not have ->mm,
that makes task_works to try to do kthread_use_mm(ctx->sqo_mm).
Don't do that if sqo_mm is NULL.
[ 290.460558] WARNING: CPU: 6 PID: 150933 at kernel/kthread.c:1238
kthread_use_mm+0xf3/0x110
[ 290.460579] CPU: 6 PID: 150933 Comm: read-write2 Tainted: G
I E 5.8.0-rc2-00066-g9b21720607cf #531
[ 290.460580] RIP: 0010:kthread_use_mm+0xf3/0x110
...
[ 290.460584] Call Trace:
[ 290.460584] __io_sq_thread_acquire_mm.isra.0.part.0+0x25/0x30
[ 290.460584] __io_req_task_submit+0x64/0x80
[ 290.460584] io_req_task_submit+0x15/0x20
[ 290.460585] task_work_run+0x67/0xa0
[ 290.460585] do_exit+0x35d/0xb70
[ 290.460585] do_group_exit+0x43/0xa0
[ 290.460585] get_signal+0x140/0x900
[ 290.460586] do_signal+0x37/0x780
[ 290.460586] __prepare_exit_to_usermode+0x126/0x1c0
[ 290.460586] __syscall_return_slowpath+0x3b/0x1c0
[ 290.460587] do_syscall_64+0x5f/0xa0
[ 290.460587] entry_SYSCALL_64_after_hwframe+0x44/0xa9
following with faults.
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
fs/io_uring.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 776f593a5bf3..c7986c27272e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -958,7 +958,7 @@ static void io_sq_thread_drop_mm(struct io_ring_ctx *ctx)
static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx)
{
if (!current->mm) {
- if (unlikely(!mmget_not_zero(ctx->sqo_mm)))
+ if (unlikely(!ctx->sqo_mm || !mmget_not_zero(ctx->sqo_mm)))
return -EFAULT;
kthread_use_mm(ctx->sqo_mm);
}
@@ -7212,10 +7212,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
{
int ret;
- mmgrab(current->mm);
- ctx->sqo_mm = current->mm;
-
if (ctx->flags & IORING_SETUP_SQPOLL) {
+ mmgrab(current->mm);
+ ctx->sqo_mm = current->mm;
+
ret = -EPERM;
if (!capable(CAP_SYS_ADMIN))
goto err;
@@ -7259,8 +7259,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
return 0;
err:
io_finish_async(ctx);
- mmdrop(ctx->sqo_mm);
- ctx->sqo_mm = NULL;
+ if (ctx->sqo_mm) {
+ mmdrop(ctx->sqo_mm);
+ ctx->sqo_mm = NULL;
+ }
return ret;
}
--
2.24.0
