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

Eric W. Biederman
2021-03-26T22:25:09Z

Jens Axboe <axboe@kernel.dk> writes:

> 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.

Gah. Kill the WARN_ON.

I was thinking "WARN_ON(!sig_kernel_fatal(ksig->sig));"
The function sig_kernel_fatal does not exist.

Fatal is the state that is left when a signal is neither
ignored nor a stop signal, and does not have a handler.

The rest of the logic still works.

Eric