Re: [PATCH 05/15] Add io_uring IO interface

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On 2019-01-17 21:50, Jeff Moyer wrote:
Jens Axboe <axboe@xxxxxxxxx> writes:

On 1/17/19 1:09 PM, Jens Axboe wrote:
On 1/17/19 1:03 PM, Jeff Moyer wrote:
Jens Axboe <axboe@xxxxxxxxx> writes:

On 1/17/19 5:48 AM, Roman Penyaev wrote:
On 2019-01-16 18:49, Jens Axboe wrote:

[...]

+static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
+				  struct io_uring_params *p)
+{
+	struct io_sq_ring *sq_ring;
+	struct io_cq_ring *cq_ring;
+	size_t size;
+	int ret;
+
+ sq_ring = io_mem_alloc(struct_size(sq_ring, array, p->sq_entries));

It seems that sq_entries, cq_entries are not limited at all. Can nasty app consume a lot of kernel pages calling io_setup_uring() from a loop
passing random entries number? (or even better: decreasing entries
number,
in order to consume all pages orders with min number of loops).

Yes, that's an oversight, we should have a limit in place. I'll add that.

Can we charge the ring memory to the RLIMIT_MEMLOCK as well? I'd prefer
not to repeat the mistake of fs.aio-max-nr.

Sure, we can do that. With the ring limited in size (it's now 4k entries at most), the amount of memory gobbled up by that is much smaller than
the fixed buffers. A max sized ring is about 256k of memory.

Per io_uring.  Nothing prevents a user from calling io_uring_setup in a
loop and continuing to gobble up memory.

What if we set a sane limit for a uring instance (not for the whole io_uring), but allocate rings on mmap? Then greedy / nasty app will be killed by oom.

--
Roman




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