On 5/27/21 9:21 AM, Olivier Langlois wrote:
> On Thu, 2021-05-27 at 07:46 -0600, Jens Axboe wrote:
>> On 5/26/21 12:21 PM, Olivier Langlois wrote:
>>> This is required for proper core dump generation.
>>>
>>> Because signals are normally serviced before resuming userspace and
>>> an
>>> io_worker thread will never resume userspace, it needs to
>>> explicitly
>>> call the signal servicing functions.
>>>
>>> Also, notice that it is possible to exit from the io_wqe_worker()
>>> function main loop while having a pending signal such as when
>>> the IO_WQ_BIT_EXIT bit is set.
>>>
>>> It is crucial to service any pending signal before calling
>>> do_exit()
>>> Proper coredump generation is relying on PF_SIGNALED to be set.
>>>
>>> More specifically, exit_mm() is using this flag to wait for the
>>> core dump completion before releasing its memory descriptor.
>>>
>>> Signed-off-by: Olivier Langlois <olivier@xxxxxxxxxxxxxx>
>>> ---
>>> fs/io-wq.c | 22 ++++++++++++++++++++--
>>> 1 file changed, 20 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>>> index 5361a9b4b47b..b76c61e9aff2 100644
>>> --- a/fs/io-wq.c
>>> +++ b/fs/io-wq.c
>>> @@ -9,8 +9,6 @@
>>> #include <linux/init.h>
>>> #include <linux/errno.h>
>>> #include <linux/sched/signal.h>
>>> -#include <linux/mm.h>
>>> -#include <linux/sched/mm.h>
>>> #include <linux/percpu.h>
>>> #include <linux/slab.h>
>>> #include <linux/rculist_nulls.h>
>>> @@ -193,6 +191,26 @@ static void io_worker_exit(struct io_worker
>>> *worker)
>>>
>>> kfree_rcu(worker, rcu);
>>> io_worker_ref_put(wqe->wq);
>>> + /*
>>> + * Because signals are normally serviced before resuming
>>> userspace and an
>>> + * io_worker thread will never resume userspace, it needs
>>> to explicitly
>>> + * call the signal servicing functions.
>>> + *
>>> + * Also notice that it is possible to exit from the
>>> io_wqe_worker()
>>> + * function main loop while having a pending signal such as
>>> when
>>> + * the IO_WQ_BIT_EXIT bit is set.
>>> + *
>>> + * It is crucial to service any pending signal before
>>> calling do_exit()
>>> + * Proper coredump generation is relying on PF_SIGNALED to
>>> be set.
>>> + *
>>> + * More specifically, exit_mm() is using this flag to wait
>>> for the
>>> + * core dump completion before releasing its memory
>>> descriptor.
>>> + */
>>> + if (signal_pending(current)) {
>>> + struct ksignal ksig;
>>> +
>>> + get_signal(&ksig);
>>> + }
>>> do_exit(0);
>>> }
>>
>> Do we need the same thing in fs/io_uring.c:io_sq_thread()?
>>
> Jens,
>
> You are 100% correct. In fact, this is the same problem for ALL
> currently existing and future io threads. Therefore, I start to think
> that the right place for the fix might be straight into do_exit()...
That is what I was getting at. To avoid poluting do_exit() with it, I
think it'd be best to add an io_thread_exit() that simply does:
void io_thread_exit(void)
{
if (signal_pending(current)) {
struct ksignal ksig;
get_signal(&ksig);
}
do_exit(0);
}
and convert the do_exit() calls in io_uring/io-wq to io_thread_exit()
instead.
--
Jens Axboe
