Re: [PATCH 2/7] io_uring: handle signals for IO threads like a normal thread

Jens Axboe
2021-03-26T22:15:24Z

On 3/26/21 2:29 PM, Eric W. Biederman wrote:
> Jens Axboe <axboe@kernel.dk> writes:
>
>> We go through various hoops to disallow signals for the IO threads, but
>> there's really no reason why we cannot just allow them. The IO threads
>> never return to userspace like a normal thread, and hence don't go through
>> normal signal processing. Instead, just check for a pending signal as part
>> of the work loop, and call get_signal() to handle it for us if anything
>> is pending.
>>
>> With that, we can support receiving signals, including special ones like
>> SIGSTOP.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> ---
>> fs/io-wq.c | 24 +++++++++++++++++-------
>> fs/io_uring.c | 12 ++++++++----
>> 2 files changed, 25 insertions(+), 11 deletions(-)
>>
>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>> index b7c1fa932cb3..3e2f059a1737 100644
>> --- a/fs/io-wq.c
>> +++ b/fs/io-wq.c
>> @@ -16,7 +16,6 @@
>> #include <linux/rculist_nulls.h>
>> #include <linux/cpu.h>
>> #include <linux/tracehook.h>
>> -#include <linux/freezer.h>
>>
>> #include "../kernel/sched/sched.h"
>> #include "io-wq.h"
>> @@ -503,10 +502,16 @@ static int io_wqe_worker(void *data)
>> if (io_flush_signals())
>> continue;
>> ret = schedule_timeout(WORKER_IDLE_TIMEOUT);
>> - if (try_to_freeze() || ret)
>> + if (signal_pending(current)) {
>> + struct ksignal ksig;
>> +
>> + if (fatal_signal_pending(current))
>> + break;
>> + if (get_signal(&ksig))
>> + continue;
> ^^^^^^^^^^^^^^^^^^^^^^
>
> That is wrong. You are promising to deliver a signal to signal
> handler and them simply discarding it. Perhaps:
>
> if (!get_signal(&ksig))
> continue;
> WARN_ON(!sig_kernel_stop(ksig->sig));
> break;

Thanks, updated.

--
Jens Axboe