From: Dylan Yudaken <dylany@meta.com>
[ upstream commit c06c6c5d27 ]
This is required for the failure case (io_req_complete_failed) and is
missing.
The alternative would be to only lock in the failure path, however all of
the non-error paths in io_poll_check_events that do not do not return
IOU_POLL_NO_ACTION end up locking anyway. The only extraneous lock would
be for the multishot poll overflowing the CQE ring, however multishot poll
would probably benefit from being locked as it will allow completions to
be batched.
So it seems reasonable to lock always.
Signed-off-by: Dylan Yudaken <dylany@meta.com>
Link: https://lore.kernel.org/r/20221124093559.3780686-3-dylany@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Commit ef7dfac51d upstream.
We selectively grab the ctx->uring_lock for poll update/removal, but
we really should grab it from the start to fully synchronize with
linked timeouts. Normally this is indeed the case, but if requests
are forced async by the application, we don't fully cover removal
and timer disarm within the uring_lock.
Make this simpler by having consistent locking state for poll removal.
Cc: stable@vger.kernel.org # 6.1+
Reported-by: Querijn Voet <querijnqyn@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 005308f7bd upstream.
Unless we have at least one entry queued, then don't call into
io_poll_remove_entries(). Normally this isn't possible, but if we
retry poll then we can have ->nr_entries cleared again as we're
setting it up. If this happens for a poll retry, then we'll still have
at least REQ_F_SINGLE_POLL set. io_poll_remove_entries() then thinks
it has entries to remove.
Clear REQ_F_SINGLE_POLL and REQ_F_DOUBLE_POLL unconditionally when
arming a poll request.
Fixes: c16bda3759 ("io_uring/poll: allow some retries for poll triggering spuriously")
Cc: stable@vger.kernel.org
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit c16bda3759 upstream.
If we get woken spuriously when polling and fail the operation with
-EAGAIN again, then we generally only allow polling again if data
had been transferred at some point. This is indicated with
REQ_F_PARTIAL_IO. However, if the spurious poll triggers when the socket
was originally empty, then we haven't transferred data yet and we will
fail the poll re-arm. This either punts the socket to io-wq if it's
blocking, or it fails the request with -EAGAIN if not. Neither condition
is desirable, as the former will slow things down, while the latter
will make the application confused.
We want to ensure that a repeated poll trigger doesn't lead to infinite
work making no progress, that's what the REQ_F_PARTIAL_IO check was
for. But it doesn't protect against a loop post the first receive, and
it's unnecessarily strict if we started out with an empty socket.
Add a somewhat random retry count, just to put an upper limit on the
potential number of retries that will be done. This should be high enough
that we won't really hit it in practice, unless something needs to be
aborted anyway.
Cc: stable@vger.kernel.org # v5.10+
Link: https://github.com/axboe/liburing/issues/364
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit df730ec21f upstream.
Fixes two errors:
"ERROR: do not use assignment in if condition
130: FILE: io_uring/net.c:130:
+ if (!(issue_flags & IO_URING_F_UNLOCKED) &&
ERROR: do not use assignment in if condition
599: FILE: io_uring/poll.c:599:
+ } else if (!(issue_flags & IO_URING_F_UNLOCKED) &&"
reported by checkpatch.pl in net.c and poll.c .
Signed-off-by: Xinghui Li <korantli@tencent.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20221102082503.32236-1-korantwork@gmail.com
[axboe: style tweaks]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 8caa03f10b upstream.
A previous commit fixed a poll race that can occur, but it's only
applicable for multishot requests. For a multishot request, we can safely
ignore a spurious wakeup, as we never leave the waitqueue to begin with.
A blunt reissue of a multishot armed request can cause us to leak a
buffer, if they are ring provided. While this seems like a bug in itself,
it's not really defined behavior to reissue a multishot request directly.
It's less efficient to do so as well, and not required to rearm anything
like it is for singleshot poll requests.
Cc: stable@vger.kernel.org
Fixes: 6e5aedb932 ("io_uring/poll: attempt request issue after racy poll wakeup")
Reported-and-tested-by: Olivier Langlois <olivier@trillion01.com>
Link: https://github.com/axboe/liburing/issues/778
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 6e5aedb932 upstream.
If we have multiple requests waiting on the same target poll waitqueue,
then it's quite possible to get a request triggered and get disappointed
in not being able to make any progress with it. If we race in doing so,
we'll potentially leave the poll request on the internal tables, but
removed from the waitqueue. That means that any subsequent trigger of
the poll waitqueue will not kick that request into action, causing an
application to potentially wait for completion of a request that will
never happen.
Fix this by adding a new poll return state, IOU_POLL_REISSUE. Rather
than have complicated logic for how to re-arm a given type of request,
just punt it for a reissue.
While in there, move the 'ret' variable to the only section where it
gets used. This avoids confusion the scope of it.
Cc: stable@vger.kernel.org
Fixes: eb0089d629 ("io_uring: single shot poll removal optimisation")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 4464853277 ]
Pass in EPOLL_URING_WAKE when signaling eventfd or doing poll related
wakups, so that we can check for a circular event dependency between
eventfd and epoll. If this flag is set when our wakeup handlers are
called, then we know we have a dependency that needs to terminate
multishot requests.
eventfd and epoll are the only such possible dependencies.
Cc: stable@vger.kernel.org # 6.0
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
There is an interesting race condition of poll_refs which could result
in a NULL pointer dereference. The crash trace is like:
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 30781 Comm: syz-executor.2 Not tainted 6.0.0-g493ffd6605b2 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:io_poll_remove_entry io_uring/poll.c:154 [inline]
RIP: 0010:io_poll_remove_entries+0x171/0x5b4 io_uring/poll.c:190
Code: ...
RSP: 0018:ffff88810dfefba0 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000040000
RDX: ffffc900030c4000 RSI: 000000000003ffff RDI: 0000000000040000
RBP: 0000000000000008 R08: ffffffff9764d3dd R09: fffffbfff3836781
R10: fffffbfff3836781 R11: 0000000000000000 R12: 1ffff11003422d60
R13: ffff88801a116b04 R14: ffff88801a116ac0 R15: dffffc0000000000
FS: 00007f9c07497700(0000) GS:ffff88811a600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffb5c00ea98 CR3: 0000000105680005 CR4: 0000000000770ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
io_apoll_task_func+0x3f/0xa0 io_uring/poll.c:299
handle_tw_list io_uring/io_uring.c:1037 [inline]
tctx_task_work+0x37e/0x4f0 io_uring/io_uring.c:1090
task_work_run+0x13a/0x1b0 kernel/task_work.c:177
get_signal+0x2402/0x25a0 kernel/signal.c:2635
arch_do_signal_or_restart+0x3b/0x660 arch/x86/kernel/signal.c:869
exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
exit_to_user_mode_prepare+0xc2/0x160 kernel/entry/common.c:201
__syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
syscall_exit_to_user_mode+0x58/0x160 kernel/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x63/0xcd
The root cause for this is a tiny overlooking in
io_poll_check_events() when cocurrently run with poll cancel routine
io_poll_cancel_req().
The interleaving to trigger use-after-free:
CPU0 | CPU1
|
io_apoll_task_func() | io_poll_cancel_req()
io_poll_check_events() |
// do while first loop |
v = atomic_read(...) |
// v = poll_refs = 1 |
... | io_poll_mark_cancelled()
| atomic_or()
| // poll_refs =
IO_POLL_CANCEL_FLAG | 1
|
atomic_sub_return(...) |
// poll_refs = IO_POLL_CANCEL_FLAG |
// loop continue |
|
| io_poll_execute()
| io_poll_get_ownership()
| // poll_refs =
IO_POLL_CANCEL_FLAG | 1
| // gets the ownership
v = atomic_read(...) |
// poll_refs not change |
|
if (v & IO_POLL_CANCEL_FLAG) |
return -ECANCELED; |
// io_poll_check_events return |
// will go into |
// io_req_complete_failed() free req |
|
| io_apoll_task_func()
| // also go into
io_req_complete_failed()
And the interleaving to trigger the kernel WARNING:
CPU0 | CPU1
|
io_apoll_task_func() | io_poll_cancel_req()
io_poll_check_events() |
// do while first loop |
v = atomic_read(...) |
// v = poll_refs = 1 |
... | io_poll_mark_cancelled()
| atomic_or()
| // poll_refs =
IO_POLL_CANCEL_FLAG | 1
|
atomic_sub_return(...) |
// poll_refs = IO_POLL_CANCEL_FLAG |
// loop continue |
|
v = atomic_read(...) |
// v = IO_POLL_CANCEL_FLAG |
| io_poll_execute()
| io_poll_get_ownership()
| // poll_refs =
IO_POLL_CANCEL_FLAG | 1
| // gets the ownership
|
WARN_ON_ONCE(!(v & IO_POLL_REF_MASK))) |
// v & IO_POLL_REF_MASK = 0 WARN |
|
| io_apoll_task_func()
| // also go into
io_req_complete_failed()
By looking up the source code and communicating with Pavel, the
implementation of this atomic poll refs should continue the loop of
io_poll_check_events() just to avoid somewhere else to grab the
ownership. Therefore, this patch simply adds another AND operation to
make sure the loop will stop if it finds the poll_refs is exactly equal
to IO_POLL_CANCEL_FLAG. Since io_poll_cancel_req() grabs ownership and
will finally make its way to io_req_complete_failed(), the req will
be reclaimed as expected.
Fixes: aa43477b04 ("io_uring: poll rework")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
[axboe: tweak description and code style]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
poll_refs carry two functions, the first is ownership over the request.
The second is notifying the io_poll_check_events() that there was an
event but wake up couldn't grab the ownership, so io_poll_check_events()
should retry.
We want to make poll_refs more robust against overflows. Instead of
always incrementing it, which covers two purposes with one atomic, check
if poll_refs is elevated enough and if so set a retry flag without
attempts to grab ownership. The gap between the bias check and following
atomics may seem racy, but we don't need it to be strict. Moreover there
might only be maximum 4 parallel updates: by the first and the second
poll entries, __io_arm_poll_handler() and cancellation. From those four,
only poll wake ups may be executed multiple times, but they're protected
by a spin.
Cc: stable@vger.kernel.org
Reported-by: Lin Ma <linma@zju.edu.cn>
Fixes: aa43477b04 ("io_uring: poll rework")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/c762bc31f8683b3270f3587691348a7119ef9c9d.1668963050.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Replace atomically substracting the ownership reference at the end of
arming a poll with a cmpxchg. We try to release ownership by setting 0
assuming that poll_refs didn't change while we were arming. If it did
change, we keep the ownership and use it to queue a tw, which is fully
capable to process all events and (even tolerates spurious wake ups).
It's a bit more elegant as we reduce races b/w setting the cancellation
flag and getting refs with this release, and with that we don't have to
worry about any kinds of underflows. It's not the fastest path for
polling. The performance difference b/w cmpxchg and atomic dec is
usually negligible and it's not the fastest path.
Cc: stable@vger.kernel.org
Fixes: aa43477b04 ("io_uring: poll rework")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0c95251624397ea6def568ff040cad2d7926fd51.1668963050.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When we post a CQE we wake all ring pollers as it normally should be.
However, if a CQE was generated by a multishot poll request targeting
its own ring, it'll wake that request up, which will make it to post
a new CQE, which will wake the request and so on until it exhausts all
CQ entries.
Don't allow multishot polling io_uring files but downgrade them to
oneshots, which was always stated as a correct behaviour that the
userspace should check for.
Cc: stable@vger.kernel.org
Fixes: aa43477b04 ("io_uring: poll rework")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3124038c0e7474d427538c2d915335ec28c92d21.1668785722.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When io_poll_check_events() collides with someone attempting to queue a
task work, it'll spin for one more time. However, it'll continue to use
the mask from the first iteration instead of updating it. For example,
if the first wake up was a EPOLLIN and the second EPOLLOUT, the
userspace will not get EPOLLOUT in time.
Clear the mask for all subsequent iterations to force vfs_poll().
Cc: stable@vger.kernel.org
Fixes: aa43477b04 ("io_uring: poll rework")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2dac97e8f691231049cb259c4ae57e79e40b537c.1668710222.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
io_poll_double_prepare() | io_poll_wake()
| poll->head = NULL
smp_load(&poll->head); /* NULL */ |
flags = req->flags; |
| req->flags &= ~SINGLE_POLL;
req->flags = flags | DOUBLE_POLL |
The idea behind io_poll_double_prepare() is to serialise with the
first poll entry by taking the wq lock. However, it's not safe to assume
that io_poll_wake() is not running when we can't grab the lock and so we
may race modifying req->flags.
Skip double poll setup if that happens. It's ok because the first poll
entry will only be removed when it's definitely completing, e.g.
pollfree or oneshot with a valid mask.
Fixes: 49f1c68e04 ("io_uring: optimise submission side poll_refs")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b7fab2d502f6121a7d7b199fe4d914a43ca9cdfd.1668184658.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stefan reports that there are issues with the level triggered
notification. Since we're late in the cycle, and it was introduced for
the 6.0 release, just disable it at prep time and we can bring this
back when Samba is happy with it.
Reported-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In preparation for adding limits, and one more user, abstract out the
core bits of the allocation+free cache.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Just as with io_poll_double_prepare() setting REQ_F_DOUBLE_POLL, we can
race with the first poll entry when setting REQ_F_ASYNC_DATA. Move it
under io_poll_double_prepare().
Fixes: a18427bb2d9b ("io_uring: optimise submission side poll_refs")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/df6920f509c11115aa2bce8b34dc5fdb0eb98920.1657203020.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
On overflow, multishot poll can still complete with the IORING_CQE_F_MORE
flag set.
If in the meantime the user clears a CQE and a the poll was cancelled then
the poll will post a CQE without the IORING_CQE_F_MORE (and likely result
-ECANCELED).
However when processing the application will encounter the non-overflow
CQE which indicates that there will be no more events posted. Typical
userspace applications would free memory associated with the poll in this
case.
It will then subsequently receive the earlier CQE which has overflowed,
which breaks the contract given by the IORING_CQE_F_MORE flag.
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220630091231.1456789-9-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Some use cases of io_post_aux_cqe would not want to overflow as is, but
might want to change the flags/result. For example multishot receive
requires in order CQE, and so if there is an overflow it would need to
stop receiving until the overflow is taken care of.
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220630091231.1456789-8-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
For multishot we want a way to signal the caller that multishot has ended
but also this might not be an error return.
For example sockets return 0 when closed, which should end a multishot
recv, but still have a CQE with result 0
Introduce IOU_STOP_MULTISHOT which does this and indicates that the return
code is stored inside req->cqe
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220630091231.1456789-7-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The values returned are a bit confusing, where 0 and 1 have implied
meaning, so add some definitions for them.
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220630091231.1456789-6-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
We really don't care about this at all in terms of performance. Outside
of having it already be marked unlikely(), shove it into a separate
__cold function.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The final poll_refs put in __io_arm_poll_handler() takes quite some
cycles. When we're arming from the original task context task_work won't
be run, so in this case we can assume that we won't race with task_works
and so not take the initial ownership ref.
One caveat is that after arming a poll we may race with it, so we have
to add a bunch of io_poll_get_ownership() hidden inside of
io_poll_can_finish_inline() whenever we want to complete arming inline.
For the same reason we can't just set REQ_F_DOUBLE_POLL in
__io_queue_proc() and so need to sync with the first poll entry by
taking its wq head lock.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8825315d7f5e182ac1578a031e546f79b1c97d01.1655990418.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
__io_arm_poll_handler() errors parsing is a horror, in case it failed it
returns 0 and the caller is expected to look at ipt.error, which already
led us to a number of problems before.
When it returns a valid mask, leave it as it's not, i.e. return 1 and
store the mask in ipt.result_mask. In case of a failure that can be
handled inline return an error code (negative value), and return 0 if
__io_arm_poll_handler() took ownership of the request and will complete
it.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/018cacdaef5fe95d7dc56b32e85d752cab7607f6.1655990418.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
io_poll_remove() expects poll_find() to search only for poll requests and
passes a flag for this. Just be a little bit extra cautious considering
lots of recent poll/cancellation changes and add a WARN_ON_ONCE checking
that we don't get an apoll'ed request.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/ec9a66f1e22f99dcd02288d4e42f3cc6bb357804.1655684496.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
clang complains on bitwise operations with bools, add a bit more
verbosity to better show that we want to call io_poll_remove_all_table()
twice but with different arguments.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f11d21dcdf9233e0eeb15fa13b858a05a78eb310.1655684496.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
We have lots of trace events accepting an io_uring request and wanting
to print some of its fields like user_data, opcode, flags and so on.
However, as trace points were unaware of io_uring structures, we had to
pass all the fields as arguments. Teach trace/events/io_uring.h about
struct io_kiocb and stop the misery of passing a horde of arguments to
trace helpers.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/40ff72f92798114e56d400f2b003beb6cde6ef53.1655384063.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently we do two extra spin lock/unlock pairs to add a poll/apoll
request to the cancellation hash table and remove it from there.
On the submission side we often already hold ->uring_lock and tw
completion is likely to hold it as well. Add a second cancellation hash
table protected by ->uring_lock. In concerns for latency because of a
need to have the mutex locked on the completion side, use the new table
only in following cases:
1) IORING_SETUP_SINGLE_ISSUER: only one task grabs uring_lock, so there
is little to no contention and so the main tw hander will almost
always end up grabbing it before calling callbacks.
2) IORING_SETUP_SQPOLL: same as with single issuer, only one task is
a major user of ->uring_lock.
3) apoll: we normally grab the lock on the completion side anyway to
execute the request, so it's free.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1bbad9c78c454b7b92f100bbf46730a37df7194f.1655371007.git.asml.silence@gmail.com
Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Instead of using implicit knowledge of what is locked or not after
io_poll_find() and co returns, pass back a pointer to the locked
bucket if any. If set the user must to unlock the spinlock.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/dae1dc5749aa34367812ecf62f82fd3f053aae44.1655371007.git.asml.silence@gmail.com
Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Add a new io_hash_bucket structure so that each bucket in cancel_hash
has separate spinlock. Use per entry lock for cancel_hash, this removes
some completion lock invocation and remove contension between different
cancel_hash entries.
Signed-off-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/05d1e135b0c8bce9d1441e6346776589e5783e26.1655371007.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
By default, the POLL_ADD command does edge triggered poll - if we get
a non-zero mask on the initial poll attempt, we complete the request
successfully.
Support level triggered by always waiting for a notification, regardless
of whether or not the initial mask matches the file state.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
