Bitfields cannot be set and checked atomically, and this makes it more
clear that these are indeed in shared storage and must be checked and
set in a sane fashion. This is in preparation for annotating a few of
the known racy, but harmless, flags checking.
No intended functional changes in this patch.
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
__io_msg_ring_data() checks that the target_ctx isn't
IORING_SETUP_R_DISABLED before calling io_msg_data_remote(), which calls
io_msg_remote_post(). So submitter_task can't be modified concurrently
with the read in io_msg_remote_post(). Additionally, submitter_task must
exist, as io_msg_data_remote() is only called for io_msg_need_remote(),
i.e. task_complete is set, which requires IORING_SETUP_DEFER_TASKRUN,
which in turn requires IORING_SETUP_SINGLE_ISSUER. And submitter_task is
assigned in io_uring_create() or io_register_enable_rings() before
enabling any IORING_SETUP_SINGLE_ISSUER io_ring_ctx.
Similarly, io_msg_send_fd() checks IORING_SETUP_R_DISABLED and
io_msg_need_remote() before calling io_msg_fd_remote(). submitter_task
therefore can't be modified concurrently with the read in
io_msg_fd_remote() and must be non-null.
io_register_enable_rings() can't run concurrently because it's called
from io_uring_register() -> __io_uring_register() with uring_lock held.
Thus, replace the READ_ONCE() and WRITE_ONCE() of submitter_task with
plain loads and stores. And remove the NULL checks of submitter_task in
io_msg_remote_post() and io_msg_fd_remote().
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
io_uring_enter(), __io_msg_ring_data(), and io_msg_send_fd() read
ctx->flags and ctx->submitter_task without holding the ctx's uring_lock.
This means they may race with the assignment to ctx->submitter_task and
the clearing of IORING_SETUP_R_DISABLED from ctx->flags in
io_register_enable_rings(). Ensure the correct ordering of the
ctx->flags and ctx->submitter_task memory accesses by storing to
ctx->flags using release ordering and loading it using acquire ordering.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: 4add705e4e ("io_uring: remove io_register_submitter")
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In preparation for uring_cmd implementations to implement functions
with the io_req_tw_func_t signature, introduce a wrapper struct
io_tw_req to hide the struct io_kiocb * argument. The intention is for
only the io_uring core to access the inner struct io_kiocb *. uring_cmd
implementations should instead call a helper from io_uring/cmd.h to
convert struct io_tw_req to struct io_uring_cmd *.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
A recent commit:
fc582cd26e ("io_uring/msg_ring: ensure io_kiocb freeing is deferred for RCU")
fixed an issue with not deferring freeing of io_kiocb structs that
msg_ring allocates to after the current RCU grace period. But this only
covers requests that don't end up in the allocation cache. If a request
goes into the alloc cache, it can get reused before it is sane to do so.
A recent syzbot report would seem to indicate that there's something
there, however it may very well just be because of the KASAN poisoning
that the alloc_cache handles manually.
Rather than attempt to make the alloc_cache sane for that use case, just
drop the usage of the alloc_cache for msg_ring request payload data.
Fixes: 50cf5f3842 ("io_uring/msg_ring: add an alloc cache for io_kiocb entries")
Link: https://lore.kernel.org/io-uring/68cc2687.050a0220.139b6.0005.GAE@google.com/
Reported-by: syzbot+baa2e0f4e02df602583e@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
syzbot reports that defer/local task_work adding via msg_ring can hit
a request that has been freed:
CPU: 1 UID: 0 PID: 19356 Comm: iou-wrk-19354 Not tainted 6.16.0-rc4-syzkaller-00108-g17bbde2e1716 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:408 [inline]
print_report+0xd2/0x2b0 mm/kasan/report.c:521
kasan_report+0x118/0x150 mm/kasan/report.c:634
io_req_local_work_add io_uring/io_uring.c:1184 [inline]
__io_req_task_work_add+0x589/0x950 io_uring/io_uring.c:1252
io_msg_remote_post io_uring/msg_ring.c:103 [inline]
io_msg_data_remote io_uring/msg_ring.c:133 [inline]
__io_msg_ring_data+0x820/0xaa0 io_uring/msg_ring.c:151
io_msg_ring_data io_uring/msg_ring.c:173 [inline]
io_msg_ring+0x134/0xa00 io_uring/msg_ring.c:314
__io_issue_sqe+0x17e/0x4b0 io_uring/io_uring.c:1739
io_issue_sqe+0x165/0xfd0 io_uring/io_uring.c:1762
io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1874
io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:642
io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:696
ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
which is supposed to be safe with how requests are allocated. But msg
ring requests alloc and free on their own, and hence must defer freeing
to a sane time.
Add an rcu_head and use kfree_rcu() in both spots where requests are
freed. Only the one in io_msg_tw_complete() is strictly required as it
has been visible on the other ring, but use it consistently in the other
spot as well.
This should not cause any other issues outside of KASAN rightfully
complaining about it.
Link: https://lore.kernel.org/io-uring/686cd2ea.a00a0220.338033.0007.GAE@google.com/
Reported-by: syzbot+54cbbfb4db9145d26fc2@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Fixes: 0617bb500b ("io_uring/msg_ring: improve handling of target CQE posting")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
IOU_COMPLETE is more descriptive, in that it explicitly says that the
return value means "please post a completion for this request". This
patch completes the transition from IOU_OK to IOU_COMPLETE, replacing
existing IOU_OK users.
This is a purely mechanical change.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In preparation for changing how io_tw_state is passed, introduce a type
alias io_tw_token_t for struct io_tw_state *. This allows for changing
the representation in one place, without having to update the many
functions that just forward their struct io_tw_state * argument.
Also add a comment to struct io_tw_state to explain its purpose.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250217022511.1150145-1-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
For remote posting of messages, req->tctx is assigned even though it
is never used. Rather than leave a dangling pointer, just clear it to
NULL and use the previous check for a valid submitter_task to gate on
whether or not the request should be terminated.
Reported-by: Jann Horn <jannh@google.com>
Fixes: b6f58a3f4a ("io_uring: move struct io_kiocb from task_struct to io_uring_task")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Rather than store the task_struct itself in struct io_kiocb, store
the io_uring specific task_struct. The life times are the same in terms
of io_uring, and this avoids doing some dereferences through the
task_struct. For the hot path of putting local task references, we can
deref req->tctx instead, which we'll need anyway in that function
regardless of whether it's local or remote references.
This is mostly straight forward, except the original task PF_EXITING
check needs a bit of tweaking. task_work is _always_ run from the
originating task, except in the fallback case, where it's run from a
kernel thread. Replace the potentially racy (in case of fallback work)
checks for req->task->flags with current->flags. It's either the still
the original task, in which case PF_EXITING will be sane, or it has
PF_KTHREAD set, in which case it's fallback work. Both cases should
prevent moving forward with the given request.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
There are lots of spots open-coding this functionality, add a generic
helper that does the node lookup in a speculation safe way.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
For files, there's nr_user_files/file_table/file_data, and buffers have
nr_user_bufs/user_bufs/buf_data. There's no reason why file_table and
file_data can't be the same thing, and ditto for the buffer side. That
gets rid of more io_ring_ctx state that's in two spots rather than just
being in one spot, as it should be. Put all the registered file data in
one locations, and ditto on the buffer front.
This also avoids having both io_rsrc_data->nodes being an allocated
array, and ->user_bufs[] or ->file_table.nodes. There's no reason to
have this information duplicated. Keep it in one spot, io_rsrc_data,
along with how many resources are available.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Normally MSG_RING requires both a source and a destination ring. But
some users don't always have a ring avilable to send a message from, yet
they still need to notify a target ring.
Add support for using io_uring_register(2) without having a source ring,
using a file descriptor of -1 for that. Internally those are called
blind registration opcodes. Implement IORING_REGISTER_SEND_MSG_RING as a
blind opcode, which simply takes an sqe that the application can put on
the stack and use the normal liburing helpers to initialize it. Then the
app can call:
io_uring_register(-1, IORING_REGISTER_SEND_MSG_RING, &sqe, 1);
and get the same behavior in terms of the target, where a CQE is posted
with the details given in the sqe.
For now this takes a single sqe pointer argument, and hence arg must
be set to that, and nr_args must be 1. Could easily be extended to take
an array of sqes, but for now let's keep it simple.
Link: https://lore.kernel.org/r/20240924115932.116167-3-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Mostly just to skip them taking an io_kiocb, rather just pass in the
ctx and io_msg directly.
In preparation for being able to issue a MSG_RING request without
having an io_kiocb. No functional changes in this patch.
Link: https://lore.kernel.org/r/20240924115932.116167-2-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
syzbot reports that KMSAN complains that 'nr_tw' is an uninit-value
with the following report:
BUG: KMSAN: uninit-value in io_req_local_work_add io_uring/io_uring.c:1192 [inline]
BUG: KMSAN: uninit-value in io_req_task_work_add_remote+0x588/0x5d0 io_uring/io_uring.c:1240
io_req_local_work_add io_uring/io_uring.c:1192 [inline]
io_req_task_work_add_remote+0x588/0x5d0 io_uring/io_uring.c:1240
io_msg_remote_post io_uring/msg_ring.c:102 [inline]
io_msg_data_remote io_uring/msg_ring.c:133 [inline]
io_msg_ring_data io_uring/msg_ring.c:152 [inline]
io_msg_ring+0x1c38/0x1ef0 io_uring/msg_ring.c:305
io_issue_sqe+0x383/0x22c0 io_uring/io_uring.c:1710
io_queue_sqe io_uring/io_uring.c:1924 [inline]
io_submit_sqe io_uring/io_uring.c:2180 [inline]
io_submit_sqes+0x1259/0x2f20 io_uring/io_uring.c:2295
__do_sys_io_uring_enter io_uring/io_uring.c:3205 [inline]
__se_sys_io_uring_enter+0x40c/0x3ca0 io_uring/io_uring.c:3142
__x64_sys_io_uring_enter+0x11f/0x1a0 io_uring/io_uring.c:3142
x64_sys_call+0x2d82/0x3c10 arch/x86/include/generated/asm/syscalls_64.h:427
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
which is the following check:
if (nr_tw < nr_wait)
return;
in io_req_local_work_add(). While nr_tw itself cannot be uninitialized,
it does depend on req->flags, which off the msg ring issue path can
indeed be uninitialized.
Fix this by always clearing the allocated 'req' fully if we can't grab
one from the cache itself.
Fixes: 50cf5f3842 ("io_uring/msg_ring: add an alloc cache for io_kiocb entries")
Reported-by: syzbot+82609b8937a4458106ca@syzkaller.appspotmail.com
Link: https://lore.kernel.org/io-uring/000000000000fd3d8d061dfc0e4a@google.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The change adding caching around the request allocated and freed for
data messages changed a kmem_cache_free() to a kfree(), which isn't
correct as the request came from slab in the first place. Fix that up
and use the right freeing function if the cache is already at its limit.
Note that the current mixing of kmem_cache_alloc and kfree is fine, but
consistent alloc/free functions should be used as it's otherwise somewhat
confusing.
Fixes: 50cf5f3842 ("io_uring/msg_ring: add an alloc cache for io_kiocb entries")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The change for improving the handling of the target CQE posting
inadvertently dropped the NULL check for the submitter task on the target
ring, reinstate that.
Fixes: 0617bb500b ("io_uring/msg_ring: improve handling of target CQE posting")
Reported-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
With slab accounting, allocating and freeing memory has considerable
overhead. Add a basic alloc cache for the io_kiocb allocations that
msg_ring needs to do. Unlike other caches, this one is used by the
sender, grabbing it from the remote ring. When the remote ring gets
the posted completion, it'll free it locally. Hence it is separately
locked, using ctx->msg_lock.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Use the exported helper for queueing task_work for message passing,
rather than rolling our own.
Note that this is only done for strict data messages for now, file
descriptor passing messages still rely on the kernel task_work. It could
get converted at some point if it's performance critical.
This improves peak performance of message passing by about 5x in some
basic testing, with 2 threads just sending messages to each other.
Before this change, it was capped at around 700K/sec, with the change
it's at over 4M/sec.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently this is gated on whether or not the target ring needs a local
completion - and if so, whether or not we're running on the right task.
The use case for same thread cross posting is probably a lot less
relevant than remote posting. And since we're going to improve this
situation anyway, just gate it on local posting and ignore what task
we're currently running on.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Jens Axboe
Caleb Sander MateosandJens Axboe
Pavel BegunkovandJens Axboe
Gabriel Krisman BertaziandJens Axboe
Al ViroandJens Axboe