linux-stable.git/fs/io_uring.c, branch linux-5.2.y

io_uring: fix wrong sequence setting logic

2019-10-05T11:13:55+00:00

[ Upstream commit 8776f3fa15a5cd213c4dfab7ddaf557983374ea6 ]

Sqo_thread will get sqring in batches, which will cause
ctx->cached_sq_head to be added in batches. if one of these
sqes is set with the DRAIN flag, then he will never get a
chance to process, and finally sqo_thread will not exit.

Fixes: de0617e4671 ("io_uring: add support for marking commands as draining")
Signed-off-by: Jackie Liu 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

io_uring: add need_resched() check in inner poll loop

2019-08-29T06:30:27+00:00

[ Upstream commit 08f5439f1df25a6cf6cf4c72cf6c13025599ce67 ]

The outer poll loop checks for whether we need to reschedule, and
returns to userspace if we do. However, it's possible to get stuck
in the inner loop as well, if the CPU we are running on needs to
reschedule to finish the IO work.

Add the need_resched() check in the inner loop as well. This fixes
a potential hang if the kernel is configured with
CONFIG_PREEMPT_VOLUNTARY=y.

Reported-by: Sagi Grimberg 
Reviewed-by: Sagi Grimberg 
Tested-by: Sagi Grimberg 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

io_uring: don't enter poll loop if we have CQEs pending

2019-08-29T06:30:27+00:00

[ Upstream commit a3a0e43fd77013819e4b6f55e37e0efe8e35d805 ]

We need to check if we have CQEs pending before starting a poll loop,
as those could be the events we will be spinning for (and hence we'll
find none). This can happen if a CQE triggers an error, or if it is
found by eg an IRQ before we get a chance to find it through polling.

Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

io_uring: fix potential hang with polled IO

2019-08-29T06:30:27+00:00

[ Upstream commit 500f9fbadef86466a435726192f4ca4df7d94236 ]

If a request issue ends up being punted to async context to avoid
blocking, we can get into a situation where the original application
enters the poll loop for that very request before it has been issued.
This should not be an issue, except that the polling will hold the
io_uring uring_ctx mutex for the duration of the poll. When the async
worker has actually issued the request, it needs to acquire this mutex
to add the request to the poll issued list. Since the application
polling is already holding this mutex, the workqueue sleeps on the
mutex forever, and the application thus never gets a chance to poll for
the very request it was interested in.

Fix this by ensuring that the polling drops the uring_ctx occasionally
if it's not making any progress.

Reported-by: Jeffrey M. Birnbaum 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

io_uring: fix manual setup of iov_iter for fixed buffers

2019-08-25T14:10:24+00:00

commit 99c79f6692ccdc42e04deea8a36e22bb48168a62 upstream.

Commit bd11b3a391e3 ("io_uring: don't use iov_iter_advance() for fixed
buffers") introduced an optimization to avoid using the slow
iov_iter_advance by manually populating the iov_iter iterator in some
cases.

However, the computation of the iterator count field was erroneous: The
first bvec was always accounted for an extent of page size even if the
bvec length was smaller.

In consequence, some I/O operations on fixed buffers were unable to
operate on the full extent of the buffer, consistently skipping some
bytes at the end of it.

Fixes: bd11b3a391e3 ("io_uring: don't use iov_iter_advance() for fixed buffers")
Cc: stable@vger.kernel.org
Signed-off-by: Aleix Roca Nonell 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

io_uring: fix KASAN use after free in io_sq_wq_submit_work

2019-08-06T17:08:19+00:00

commit d0ee879187df966ef638031b5f5183078d672141 upstream.

[root@localhost ~]# ./liburing/test/link

QEMU Standard PC report that:

[   29.379892] CPU: 0 PID: 84 Comm: kworker/u2:2 Not tainted 5.3.0-rc2-00051-g4010b622f1d2-dirty #86
[   29.379902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
[   29.379913] Workqueue: io_ring-wq io_sq_wq_submit_work
[   29.379929] Call Trace:
[   29.379953]  dump_stack+0xa9/0x10e
[   29.379970]  ? io_sq_wq_submit_work+0xbf4/0xe90
[   29.379986]  print_address_description.cold.6+0x9/0x317
[   29.379999]  ? io_sq_wq_submit_work+0xbf4/0xe90
[   29.380010]  ? io_sq_wq_submit_work+0xbf4/0xe90
[   29.380026]  __kasan_report.cold.7+0x1a/0x34
[   29.380044]  ? io_sq_wq_submit_work+0xbf4/0xe90
[   29.380061]  kasan_report+0xe/0x12
[   29.380076]  io_sq_wq_submit_work+0xbf4/0xe90
[   29.380104]  ? io_sq_thread+0xaf0/0xaf0
[   29.380152]  process_one_work+0xb59/0x19e0
[   29.380184]  ? pwq_dec_nr_in_flight+0x2c0/0x2c0
[   29.380221]  worker_thread+0x8c/0xf40
[   29.380248]  ? __kthread_parkme+0xab/0x110
[   29.380265]  ? process_one_work+0x19e0/0x19e0
[   29.380278]  kthread+0x30b/0x3d0
[   29.380292]  ? kthread_create_on_node+0xe0/0xe0
[   29.380311]  ret_from_fork+0x3a/0x50

[   29.380635] Allocated by task 209:
[   29.381255]  save_stack+0x19/0x80
[   29.381268]  __kasan_kmalloc.constprop.6+0xc1/0xd0
[   29.381279]  kmem_cache_alloc+0xc0/0x240
[   29.381289]  io_submit_sqe+0x11bc/0x1c70
[   29.381300]  io_ring_submit+0x174/0x3c0
[   29.381311]  __x64_sys_io_uring_enter+0x601/0x780
[   29.381322]  do_syscall_64+0x9f/0x4d0
[   29.381336]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

[   29.381633] Freed by task 84:
[   29.382186]  save_stack+0x19/0x80
[   29.382198]  __kasan_slab_free+0x11d/0x160
[   29.382210]  kmem_cache_free+0x8c/0x2f0
[   29.382220]  io_put_req+0x22/0x30
[   29.382230]  io_sq_wq_submit_work+0x28b/0xe90
[   29.382241]  process_one_work+0xb59/0x19e0
[   29.382251]  worker_thread+0x8c/0xf40
[   29.382262]  kthread+0x30b/0x3d0
[   29.382272]  ret_from_fork+0x3a/0x50

[   29.382569] The buggy address belongs to the object at ffff888067172140
                which belongs to the cache io_kiocb of size 224
[   29.384692] The buggy address is located 120 bytes inside of
                224-byte region [ffff888067172140, ffff888067172220)
[   29.386723] The buggy address belongs to the page:
[   29.387575] page:ffffea00019c5c80 refcount:1 mapcount:0 mapping:ffff88806ace5180 index:0x0
[   29.387587] flags: 0x100000000000200(slab)
[   29.387603] raw: 0100000000000200 dead000000000100 dead000000000122 ffff88806ace5180
[   29.387617] raw: 0000000000000000 00000000800c000c 00000001ffffffff 0000000000000000
[   29.387624] page dumped because: kasan: bad access detected

[   29.387920] Memory state around the buggy address:
[   29.388771]  ffff888067172080: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
[   29.390062]  ffff888067172100: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
[   29.391325] >ffff888067172180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[   29.392578]                                         ^
[   29.393480]  ffff888067172200: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
[   29.394744]  ffff888067172280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   29.396003] ==================================================================
[   29.397260] Disabling lock debugging due to kernel taint

io_sq_wq_submit_work free and read req again.

Cc: Zhengyuan Liu 
Cc: linux-block@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: f7b76ac9d17e ("io_uring: fix counter inc/dec mismatch in async_list")
Signed-off-by: Jackie Liu 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

io_uring: don't use iov_iter_advance() for fixed buffers

2019-07-31T05:25:03+00:00

commit bd11b3a391e3df6fa958facbe4b3f9f4cca9bd49 upstream.

Hrvoje reports that when a large fixed buffer is registered and IO is
being done to the latter pages of said buffer, the IO submission time
is much worse:

reading to the start of the buffer: 11238 ns
reading to the end of the buffer:   1039879 ns

In fact, it's worse by two orders of magnitude. The reason for that is
how io_uring figures out how to setup the iov_iter. We point the iter
at the first bvec, and then use iov_iter_advance() to fast-forward to
the offset within that buffer we need.

However, that is abysmally slow, as it entails iterating the bvecs
that we setup as part of buffer registration. There's really no need
to use this generic helper, as we know it's a BVEC type iterator, and
we also know that each bvec is PAGE_SIZE in size, apart from possibly
the first and last. Hence we can just use a shift on the offset to
find the right index, and then adjust the iov_iter appropriately.
After this fix, the timings are:

reading to the start of the buffer: 10135 ns
reading to the end of the buffer:   1377 ns

Or about an 755x improvement for the tail page.

Reported-by: Hrvoje Zeba 
Tested-by: Hrvoje Zeba 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

io_uring: fix counter inc/dec mismatch in async_list

2019-07-31T05:25:03+00:00

commit f7b76ac9d17e16e44feebb6d2749fec92bfd6dd4 upstream.

We could queue a work for each req in defer and link list without
increasing async_list->cnt, so we shouldn't decrease it while exiting
from workqueue as well if we didn't process the req in async list.

Thanks to Jens Axboe  for his guidance.

Fixes: 31b515106428 ("io_uring: allow workqueue item to handle multiple buffered requests")
Signed-off-by: Zhengyuan Liu 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

io_uring: ensure ->list is initialized for poll commands

2019-07-31T05:25:03+00:00

commit 36703247d5f52a679df9da51192b6950fe81689f upstream.

Daniel reports that when testing an http server that uses io_uring
to poll for incoming connections, sometimes it hard crashes. This is
due to an uninitialized list member for the io_uring request. Normally
this doesn't trigger and none of the test cases caught it.

Reported-by: Daniel Kozak 
Tested-by: Daniel Kozak 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

io_uring: add a memory barrier before atomic_read

2019-07-31T05:25:03+00:00

commit c0e48f9dea9129aa11bec3ed13803bcc26e96e49 upstream.

There is a hang issue while using fio to do some basic test. The issue
can be easily reproduced using the below script:

        while true
        do
                fio  --ioengine=io_uring  -rw=write -bs=4k -numjobs=1 \
                     -size=1G -iodepth=64 -name=uring   --filename=/dev/zero
        done

After several minutes (or more), fio would block at
io_uring_enter->io_cqring_wait in order to waiting for previously
committed sqes to be completed and can't return to user anymore until
we send a SIGTERM to fio. After receiving SIGTERM, fio hangs at
io_ring_ctx_wait_and_kill with a backtrace like this:

        [54133.243816] Call Trace:
        [54133.243842]  __schedule+0x3a0/0x790
        [54133.243868]  schedule+0x38/0xa0
        [54133.243880]  schedule_timeout+0x218/0x3b0
        [54133.243891]  ? sched_clock+0x9/0x10
        [54133.243903]  ? wait_for_completion+0xa3/0x130
        [54133.243916]  ? _raw_spin_unlock_irq+0x2c/0x40
        [54133.243930]  ? trace_hardirqs_on+0x3f/0xe0
        [54133.243951]  wait_for_completion+0xab/0x130
        [54133.243962]  ? wake_up_q+0x70/0x70
        [54133.243984]  io_ring_ctx_wait_and_kill+0xa0/0x1d0
        [54133.243998]  io_uring_release+0x20/0x30
        [54133.244008]  __fput+0xcf/0x270
        [54133.244029]  ____fput+0xe/0x10
        [54133.244040]  task_work_run+0x7f/0xa0
        [54133.244056]  do_exit+0x305/0xc40
        [54133.244067]  ? get_signal+0x13b/0xbd0
        [54133.244088]  do_group_exit+0x50/0xd0
        [54133.244103]  get_signal+0x18d/0xbd0
        [54133.244112]  ? _raw_spin_unlock_irqrestore+0x36/0x60
        [54133.244142]  do_signal+0x34/0x720
        [54133.244171]  ? exit_to_usermode_loop+0x7e/0x130
        [54133.244190]  exit_to_usermode_loop+0xc0/0x130
        [54133.244209]  do_syscall_64+0x16b/0x1d0
        [54133.244221]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The reason is that we had added a req to ctx->pending_async at the very
end, but it didn't get a chance to be processed. How could this happen?

        fio#cpu0                                        wq#cpu1

        io_add_to_prev_work                    io_sq_wq_submit_work

          atomic_read() <<< 1

                                                  atomic_dec_return() << 1->0
                                                  list_empty();    <<< true;

          list_add_tail()
          atomic_read() << 0 or 1?

As atomic_ops.rst states, atomic_read does not guarantee that the
runtime modification by any other thread is visible yet, so we must take
care of that with a proper implicit or explicit memory barrier.

This issue was detected with the help of Jackie's 

Fixes: 31b515106428 ("io_uring: allow workqueue item to handle multiple buffered requests")
Signed-off-by: Zhengyuan Liu 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman