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

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Message-ID: <106a38d3-5a5f-17fd-41f7-890f5e9a3602@kernel.dk>
Date:   Fri, 26 Mar 2021 16:14:48 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     io-uring@...r.kernel.org, torvalds@...ux-foundation.org,
        metze@...ba.org, oleg@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] io_uring: handle signals for IO threads like a normal
 thread

On 3/26/21 2:29 PM, Eric W. Biederman wrote:
> Jens Axboe <axboe@...nel.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@...nel.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