Re: [PATCH] io_uring: use cpu_online() to check p->sq_thread_cpu instead of cpu_possible()

From: Jens Axboe <axboe@kernel.dk>
To: Jeff Moyer <jmoyer@redhat.com>, Shenghui Wang <shhuiw@foxmail.com>
Cc: viro@zeniv.linux.org.uk, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] io_uring: use cpu_online() to check p->sq_thread_cpu instead of cpu_possible()
Date: Wed, 1 May 2019 08:15:33 -0600	[thread overview]
Message-ID: <cd55b1e4-9395-a8b7-707e-ceed9d6c0c15@kernel.dk> (raw)
In-Reply-To: <x49wojaxuaa.fsf@segfault.boston.devel.redhat.com>

On 5/1/19 5:56 AM, Jeff Moyer wrote:
> Shenghui Wang <shhuiw@foxmail.com> writes:
> 
>> This issue is found by running liburing/test/io_uring_setup test.
>>
>> When test run, the testcase "attempt to bind to invalid cpu" would not
>> pass with messages like:
>>    io_uring_setup(1, 0xbfc2f7c8), \
>> flags: IORING_SETUP_SQPOLL|IORING_SETUP_SQ_AFF, \
>> resv: 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000, \
>> sq_thread_cpu: 2
>>    expected -1, got 3
>>    FAIL
>>
>> On my system, there is:
>>    CPU(s) possible : 0-3
>>    CPU(s) online   : 0-1
>>    CPU(s) offline  : 2-3
>>    CPU(s) present  : 0-1
>>
>> The sq_thread_cpu 2 is offline on my system, so the bind should fail.
>> But cpu_possible() will pass the check. We shouldn't be able to bind
>> to an offline cpu. Use cpu_online() to do the check.
>>
>> After the change, the testcase run as expected: EINVAL will be returned
>> for cpu offlined.
>>
>> Signed-off-by: Shenghui Wang <shhuiw@foxmail.com>
>> ---
>>  fs/io_uring.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 0e9fb2cb1984..aa3d39860a1c 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -2241,7 +2241,7 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
>>  	ctx->sqo_mm = current->mm;
>>  
>>  	ret = -EINVAL;
>> -	if (!cpu_possible(p->sq_thread_cpu))
>> +	if (!cpu_online(p->sq_thread_cpu))
>>  		goto err;
>>  
>>  	if (ctx->flags & IORING_SETUP_SQPOLL) {
>> @@ -2258,7 +2258,7 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
>>  
>>  			cpu = array_index_nospec(p->sq_thread_cpu, NR_CPUS);
>>  			ret = -EINVAL;
>> -			if (!cpu_possible(p->sq_thread_cpu))
>> +			if (!cpu_online(p->sq_thread_cpu))
>>  				goto err;
>>  
>>  			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
> 
> Hmm.  Why are we doing this check twice?  Oh... Jens, I think you
> braino'd commit 917257daa0fea.  Have a look.  You probably wanted to get
> rid of the first check for cpu_possible.

Added a fixup patch the other day:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=362bf8670efccebca22efda1ee5a5ee831ec5efb

-- 
Jens Axboe