linux/io_uring/io_uring.c, branch v6.7

io_uring: fix mutex_unlock with unreferenced ctx

2023-12-04T02:09:28Z

Callers of mutex_unlock() have to make sure that the mutex stays alive for the whole duration of the function call. For io_uring that means that the following pattern is not valid unless we ensure that the context outlives the mutex_unlock() call. mutex_lock(&ctx->uring_lock); req_put(req); // typically via io_req_task_submit() mutex_unlock(&ctx->uring_lock); Most contexts are fine: io-wq pins requests, syscalls hold the file, task works are taking ctx references and so on. However, the task work fallback path doesn't follow the rule. Cc: Fixes: 04fc6c802d ("io_uring: save ctx put/get for task_work submit") Reported-by: Jann Horn Signed-off-by: Pavel Begunkov Link: https://lore.kernel.org/io-uring/CAG48ez3xSoYb+45f1RLtktROJrpiDQ1otNvdR+YLQf7m+Krj5Q@mail.gmail.com/ Signed-off-by: Jens Axboe

io_uring: use fget/fput consistently

2023-11-28T18:56:29Z

Normally within a syscall it's fine to use fdget/fdput for grabbing a file from the file table, and it's fine within io_uring as well. We do that via io_uring_enter(2), io_uring_register(2), and then also for cancel which is invoked from the latter. io_uring cannot close its own file descriptors as that is explicitly rejected, and for the cancel side of things, the file itself is just used as a lookup cookie. However, it is more prudent to ensure that full references are always grabbed. For anything threaded, either explicitly in the application itself or through use of the io-wq worker threads, this is what happens anyway. Generalize it and use fget/fput throughout. Also see the below link for more details. Link: https://lore.kernel.org/io-uring/CAG48ez1htVSO3TqmrF8QcX2WFuYTRM-VZ_N10i-VZgbtg=NNqw@mail.gmail.com/ Suggested-by: Jann Horn Signed-off-by: Jens Axboe

io_uring: free io_buffer_list entries via RCU

2023-11-28T18:45:02Z

mmap_lock nests under uring_lock out of necessity, as we may be doing user copies with uring_lock held. However, for mmap of provided buffer rings, we attempt to grab uring_lock with mmap_lock already held from do_mmap(). This makes lockdep, rightfully, complain: WARNING: possible circular locking dependency detected 6.7.0-rc1-00009-gff3337ebaf94-dirty #4438 Not tainted ------------------------------------------------------ buf-ring.t/442 is trying to acquire lock: ffff00020e1480a8 (&ctx->uring_lock){+.+.}-{3:3}, at: io_uring_validate_mmap_request.isra.0+0x4c/0x140 but task is already holding lock: ffff0000dc226190 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x124/0x264 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_lock){++++}-{3:3}: __might_fault+0x90/0xbc io_register_pbuf_ring+0x94/0x488 __arm64_sys_io_uring_register+0x8dc/0x1318 invoke_syscall+0x5c/0x17c el0_svc_common.constprop.0+0x108/0x130 do_el0_svc+0x2c/0x38 el0_svc+0x4c/0x94 el0t_64_sync_handler+0x118/0x124 el0t_64_sync+0x168/0x16c -> #0 (&ctx->uring_lock){+.+.}-{3:3}: __lock_acquire+0x19a0/0x2d14 lock_acquire+0x2e0/0x44c __mutex_lock+0x118/0x564 mutex_lock_nested+0x20/0x28 io_uring_validate_mmap_request.isra.0+0x4c/0x140 io_uring_mmu_get_unmapped_area+0x3c/0x98 get_unmapped_area+0xa4/0x158 do_mmap+0xec/0x5b4 vm_mmap_pgoff+0x158/0x264 ksys_mmap_pgoff+0x1d4/0x254 __arm64_sys_mmap+0x80/0x9c invoke_syscall+0x5c/0x17c el0_svc_common.constprop.0+0x108/0x130 do_el0_svc+0x2c/0x38 el0_svc+0x4c/0x94 el0t_64_sync_handler+0x118/0x124 el0t_64_sync+0x168/0x16c From that mmap(2) path, we really just need to ensure that the buffer list doesn't go away from underneath us. For the lower indexed entries, they never go away until the ring is freed and we can always sanely reference those as long as the caller has a file reference. For the higher indexed ones in our xarray, we just need to ensure that the buffer list remains valid while we return the address of it. Free the higher indexed io_buffer_list entries via RCU. With that we can avoid needing ->uring_lock inside mmap(2), and simply hold the RCU read lock around the buffer list lookup and address check. To ensure that the arrayed lookup either returns a valid fully formulated entry via RCU lookup, add an 'is_ready' flag that we access with store and release memory ordering. This isn't needed for the xarray lookups, but doesn't hurt either. Since this isn't a fast path, retain it across both types. Similarly, for the allocated array inside the ctx, ensure we use the proper load/acquire as setup could in theory be running in parallel with mmap. While in there, add a few lockdep checks for documentation purposes. Cc: stable@vger.kernel.org Fixes: c56e022c0a27 ("io_uring: add support for user mapped provided buffer ring") Signed-off-by: Jens Axboe

io_uring/kbuf: defer release of mapped buffer rings

2023-11-28T14:56:16Z

If a provided buffer ring is setup with IOU_PBUF_RING_MMAP, then the kernel allocates the memory for it and the application is expected to mmap(2) this memory. However, io_uring uses remap_pfn_range() for this operation, so we cannot rely on normal munmap/release on freeing them for us. Stash an io_buf_free entry away for each of these, if any, and provide a helper to free them post ->release(). Cc: stable@vger.kernel.org Fixes: c56e022c0a27 ("io_uring: add support for user mapped provided buffer ring") Reported-by: Jann Horn Signed-off-by: Jens Axboe

io_uring: enable io_mem_alloc/free to be used in other parts

2023-11-28T03:53:52Z

In preparation for using these helpers, make them non-static and add them to our internal header. Signed-off-by: Jens Axboe

io_uring: don't guard IORING_OFF_PBUF_RING with SETUP_NO_MMAP

2023-11-28T00:10:56Z

This flag only applies to the SQ and CQ rings, it's perfectly valid to use a mmap approach for the provided ring buffers. Move the check into where it belongs. Cc: stable@vger.kernel.org Fixes: 03d89a2de25b ("io_uring: support for user allocated memory for rings/sqes") Signed-off-by: Jens Axboe

io_uring: don't allow discontig pages for IORING_SETUP_NO_MMAP

2023-11-27T15:28:56Z

io_sqes_map() is used rather than io_mem_alloc(), if the application passes in memory for mapping rather than have the kernel allocate it and then mmap(2) the ranges. This then calls __io_uaddr_map() to perform the page mapping and pinning, which checks if we end up with the same pages, if more than one page is mapped. But this check is incorrect and only checks if the first and last pages are the same, where it really should be checking if the mapped pages are contigous. This allows mapping a single normal page, or a huge page range. Down the line we can add support for remapping pages to be virtually contigous, which is really all that io_uring cares about. Cc: stable@vger.kernel.org Fixes: 03d89a2de25b ("io_uring: support for user allocated memory for rings/sqes") Reported-by: Jann Horn Signed-off-by: Jens Axboe

Merge tag 'io_uring-futex-2023-10-30' of git://git.kernel.dk/linux

2023-11-01T21:25:08Z

Pull io_uring futex support from Jens Axboe: "This adds support for using futexes through io_uring - first futex wake and wait, and then the vectored variant of waiting, futex waitv. For both wait/wake/waitv, we support the bitset variant, as the 'normal' variants can be easily implemented on top of that. PI and requeue are not supported through io_uring, just the above mentioned parts. This may change in the future, but in the spirit of keeping this small (and based on what people have been asking for), this is what we currently have. Wake support is pretty straight forward, most of the thought has gone into the wait side to avoid needing to offload wait operations to a blocking context. Instead, we rely on the usual callbacks to retry and post a completion event, when appropriate. As far as I can recall, the first request for futex support with io_uring came from Andres Freund, working on postgres. His aio rework of postgres was one of the early adopters of io_uring, and futex support was a natural extension for that. This is relevant from both a usability point of view, as well as for effiency and performance. In Andres's words, for the former: Futex wait support in io_uring makes it a lot easier to avoid deadlocks in concurrent programs that have their own buffer pool: Obviously pages in the application buffer pool have to be locked during IO. If the initiator of IO A needs to wait for a held lock B, the holder of lock B might wait for the IO A to complete. The ability to wait for a lock and IO completions at the same time provides an efficient way to avoid such deadlocks and in terms of effiency, even without unlocking the full potential yet, Andres says: Futex wake support in io_uring is useful because it allows for more efficient directed wakeups. For some "locks" postgres has queues implemented in userspace, with wakeup logic that cannot easily be implemented with FUTEX_WAKE_BITSET on a single "futex word" (imagine waiting for journal flushes to have completed up to a certain point). Thus a "lock release" sometimes need to wake up many processes in a row. A quick-and-dirty conversion to doing these wakeups via io_uring lead to a 3% throughput increase, with 12% fewer context switches, albeit in a fairly extreme workload" * tag 'io_uring-futex-2023-10-30' of git://git.kernel.dk/linux: io_uring: add support for vectored futex waits futex: make the vectored futex operations available futex: make futex_parse_waitv() available as a helper futex: add wake_data to struct futex_q io_uring: add support for futex wake and wait futex: abstract out a __futex_wake_mark() helper futex: factor out the futex wake handling futex: move FUTEX2_VALID_MASK to futex.h

Merge tag 'for-6.7/io_uring-2023-10-30' of git://git.kernel.dk/linux

2023-11-01T21:09:19Z

Pull io_uring updates from Jens Axboe: "This contains the core io_uring updates, of which there are not many, and adds support for using WAITID through io_uring and hence not needing to block on these kinds of events. Outside of that, tweaks to the legacy provided buffer handling and some cleanups related to cancelations for uring_cmd support" * tag 'for-6.7/io_uring-2023-10-30' of git://git.kernel.dk/linux: io_uring/poll: use IOU_F_TWQ_LAZY_WAKE for wakeups io_uring/kbuf: Use slab for struct io_buffer objects io_uring/kbuf: Allow the full buffer id space for provided buffers io_uring/kbuf: Fix check of BID wrapping in provided buffers io_uring/rsrc: cleanup io_pin_pages() io_uring: cancelable uring_cmd io_uring: retain top 8bits of uring_cmd flags for kernel internal use io_uring: add IORING_OP_WAITID support exit: add internal include file with helpers exit: add kernel_waitid_prepare() helper exit: move core of do_wait() into helper exit: abstract out should_wake helper for child_wait_callback() io_uring/rw: add support for IORING_OP_READ_MULTISHOT io_uring/rw: mark readv/writev as vectored in the opcode definition io_uring/rw: split io_read() into a helper

io_uring: fix crash with IORING_SETUP_NO_MMAP and invalid SQ ring address

2023-10-18T15:22:14Z

If we specify a valid CQ ring address but an invalid SQ ring address, we'll correctly spot this and free the allocated pages and clear them to NULL. However, we don't clear the ring page count, and hence will attempt to free the pages again. We've already cleared the address of the page array when freeing them, but we don't check for that. This causes the following crash: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Oops [#1] Modules linked in: CPU: 0 PID: 20 Comm: kworker/u2:1 Not tainted 6.6.0-rc5-dirty #56 Hardware name: ucbbar,riscvemu-bare (DT) Workqueue: events_unbound io_ring_exit_work epc : io_pages_free+0x2a/0x58 ra : io_rings_free+0x3a/0x50 epc : ffffffff808811a2 ra : ffffffff80881406 sp : ffff8f80000c3cd0 status: 0000000200000121 badaddr: 0000000000000000 cause: 000000000000000d [] io_pages_free+0x2a/0x58 [] io_rings_free+0x3a/0x50 [] io_ring_exit_work+0x37e/0x424 [] process_one_work+0x10c/0x1f4 [] worker_thread+0x252/0x31c [] kthread+0xc4/0xe0 [] ret_from_fork+0xa/0x1c Check for a NULL array in io_pages_free(), but also clear the page counts when we free them to be on the safer side. Reported-by: rtm@csail.mit.edu Fixes: 03d89a2de25b ("io_uring: support for user allocated memory for rings/sqes") Cc: stable@vger.kernel.org Reviewed-by: Jeff Moyer Signed-off-by: Jens Axboe