| Message ID | 20241112163021.1948119-1-maharmstone@fb.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | btrfs: add io_uring interface for encoded writes | expand |
On 11/12/24 9:29 AM, Mark Harmstone wrote: > Add an io_uring interface for encoded writes, with the same parameters > as the BTRFS_IOC_ENCODED_WRITE ioctl. > > As with the encoded reads code, there's a test program for this at > https://github.com/maharmstone/io_uring-encoded, and I'll get this > worked into an fstest. > > How io_uring works is that it initially calls btrfs_uring_cmd with the > IO_URING_F_NONBLOCK flag set, and if we return -EAGAIN it tries again in > a kthread with the flag cleared. ^^^^^^^^ Not a kernel thread, it's an io worker. The distinction may seem irrelevant, but it's really not - io workers inherit all the properties of the original task. > Ideally we'd honour this and call try_lock etc., but there's still a lot > of work to be done to create non-blocking versions of all the functions > in our write path. Instead, just validate the input in > btrfs_uring_encoded_write() on the first pass and return -EAGAIN, with a > view to properly optimizing the happy path later on. But you need to ensure stable state after the first issue, regardless of how you handle it. I don't have the other patches handy, but whatever you copy from userspace before you return -EAGAIN, you should not be copying again. By the time you get the 2nd invocation from io-wq, no copying should be taking place, you should be using the state you already ensured was stable for the non-blocking issue. Maybe this is all handled by the caller of btrfs_uring_encoded_write() already? As far as looking at the code below, it just looks like it copies everything, then returns -EAGAIN, then copies it again later? Yes uring_cmd will make the sqe itself stable, but: sqe_addr = u64_to_user_ptr(READ_ONCE(cmd->sqe->addr)); the userspace btrfs_ioctl_encoded_io_args that sqe->addr points too should remain stable as well. If not, consider userspace doing: some_func() { struct btrfs_ioctl_encoded_io_args args; fill_in_args(&args); sqe = io_uring_get_sqe(ring); sqe->addr = &args; io_uring_submit(); <- initial invocation here } main_func() { some_func(); - io-wq invocation perhaps here wait_on_cqes(); } where io-wq will be reading garbage as args went out of scope, unless some_func() used a stable/heap struct that isn't freed until completion. some_func() can obviously wait on the cqe, but at that point you'd be using it as a sync interface, and there's little point. This is why io_kiocb->async_data exists. uring_cmd is already using that for the sqe, I think you'd want to add a 2nd "void *op_data" or something in there, and have the uring_cmd alloc cache get clear that to NULL and have uring_cmd alloc cache put kfree() it if it's non-NULL. We'd also need to move the uring_cache struct into include/linux/io_uring_types.h so that btrfs can get to it (and probably rename it to something saner, uring_cmd_async_data for example). static int btrfs_uring_encoded_write(struct io_uring_cmd *cmd, unsigned int issue_flags) { struct io_kiocb *req = cmd_to_io_kiocb(cmd); struct uring_cmd_async_data *data = req->async_data; struct btrfs_ioctl_encoded_io_args *args; if (!data->op_data) { data->op_data = kmalloc(sizeof(*args), GFP_NOIO); if (!data->op_data) return -ENOMEM; if (copy_from_user(data->op_data, sqe_addr, sizeof(*args)) return -EFAULT; } ... } and have it be stable, then moving your copying into a helper rather than inline in btrfs_uring_encoded_write() (it probably should be regardless). Ignored the compat above, it's just pseudo code. Anyway, hope that helps. I'll be happy to do the uring_cmd bit for you, but it really should be pretty straight forward. I'm also pondering if the encoded read side suffers from the same issue?
On 11/12/24 2:01 PM, Jens Axboe wrote: > This is why io_kiocb->async_data exists. uring_cmd is already using that > for the sqe, I think you'd want to add a 2nd "void *op_data" or > something in there, and have the uring_cmd alloc cache get clear that to > NULL and have uring_cmd alloc cache put kfree() it if it's non-NULL. > > We'd also need to move the uring_cache struct into > include/linux/io_uring_types.h so that btrfs can get to it (and probably > rename it to something saner, uring_cmd_async_data for example). Here are two patches that implement that basic thing on the io_uring uring_cmd side. With that, you can then do: > static int btrfs_uring_encoded_write(struct io_uring_cmd *cmd, unsigned int issue_flags) > { > struct io_kiocb *req = cmd_to_io_kiocb(cmd); > struct uring_cmd_async_data *data = req->async_data; > struct btrfs_ioctl_encoded_io_args *args; > > if (!data->op_data) { > data->op_data = kmalloc(sizeof(*args), GFP_NOIO); > if (!data->op_data) > return -ENOMEM; > if (copy_from_user(data->op_data, sqe_addr, sizeof(*args)) > return -EFAULT; > } > ... > } and have it be both stable, and not need to worry about freeing it either. Hope that helps. Totally untested...
On 11/12/24 2:01 PM, Jens Axboe wrote:
> I'm also pondering if the encoded read side suffers from the same issue?
It does, it needs the same fixup.
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 6478216305c7..37578270686a 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -5030,6 +5030,116 @@ static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd, unsigned int issue return ret; } +static int btrfs_uring_encoded_write(struct io_uring_cmd *cmd, unsigned int issue_flags) +{ + struct btrfs_ioctl_encoded_io_args args; + struct iovec iovstack[UIO_FASTIOV]; + struct iovec *iov = iovstack; + struct iov_iter iter; + loff_t pos; + struct kiocb kiocb; + struct file *file; + ssize_t ret; + void __user *sqe_addr; + + if (!capable(CAP_SYS_ADMIN)) { + ret = -EPERM; + goto out_acct; + } + + file = cmd->file; + sqe_addr = u64_to_user_ptr(READ_ONCE(cmd->sqe->addr)); + + if (!(file->f_mode & FMODE_WRITE)) { + ret = -EBADF; + goto out_acct; + } + + if (issue_flags & IO_URING_F_COMPAT) { +#if defined(CONFIG_64BIT) && defined(CONFIG_COMPAT) + struct btrfs_ioctl_encoded_io_args_32 args32; + + if (copy_from_user(&args32, sqe_addr, sizeof(args32))) { + ret = -EFAULT; + goto out_acct; + } + args.iov = compat_ptr(args32.iov); + args.iovcnt = args32.iovcnt; + args.offset = args32.offset; + args.flags = args32.flags; + args.len = args32.len; + args.unencoded_len = args32.unencoded_len; + args.unencoded_offset = args32.unencoded_offset; + args.compression = args32.compression; + args.encryption = args32.encryption; + memcpy(args.reserved, args32.reserved, sizeof(args.reserved)); +#else + return -ENOTTY; +#endif + } else { + if (copy_from_user(&args, sqe_addr, sizeof(args))) { + ret = -EFAULT; + goto out_acct; + } + } + + ret = -EINVAL; + if (args.flags != 0) + goto out_acct; + if (memchr_inv(args.reserved, 0, sizeof(args.reserved))) + goto out_acct; + if (args.compression == BTRFS_ENCODED_IO_COMPRESSION_NONE && + args.encryption == BTRFS_ENCODED_IO_ENCRYPTION_NONE) + goto out_acct; + if (args.compression >= BTRFS_ENCODED_IO_COMPRESSION_TYPES || + args.encryption >= BTRFS_ENCODED_IO_ENCRYPTION_TYPES) + goto out_acct; + if (args.unencoded_offset > args.unencoded_len) + goto out_acct; + if (args.len > args.unencoded_len - args.unencoded_offset) + goto out_acct; + + if (issue_flags & IO_URING_F_NONBLOCK) { + ret = -EAGAIN; + goto out_acct; + } + + ret = import_iovec(ITER_SOURCE, args.iov, args.iovcnt, ARRAY_SIZE(iovstack), + &iov, &iter); + if (ret < 0) + goto out_acct; + + if (iov_iter_count(&iter) == 0) { + ret = 0; + goto out_iov; + } + pos = args.offset; + ret = rw_verify_area(WRITE, file, &pos, args.len); + if (ret < 0) + goto out_iov; + + init_sync_kiocb(&kiocb, file); + ret = kiocb_set_rw_flags(&kiocb, 0, WRITE); + if (ret) + goto out_iov; + kiocb.ki_pos = pos; + + file_start_write(file); + + ret = btrfs_do_write_iter(&kiocb, &iter, &args); + if (ret > 0) + fsnotify_modify(file); + + file_end_write(file); +out_iov: + kfree(iov); +out_acct: + if (ret > 0) + add_wchar(current, ret); + inc_syscw(current); + return ret; +} + int btrfs_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) { switch (cmd->cmd_op) { @@ -5038,6 +5148,12 @@ int btrfs_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) case BTRFS_IOC_ENCODED_READ_32: #endif return btrfs_uring_encoded_read(cmd, issue_flags); + + case BTRFS_IOC_ENCODED_WRITE: +#if defined(CONFIG_64BIT) && defined(CONFIG_COMPAT) + case BTRFS_IOC_ENCODED_WRITE_32: +#endif + return btrfs_uring_encoded_write(cmd, issue_flags); } return -EINVAL;
Add an io_uring interface for encoded writes, with the same parameters as the BTRFS_IOC_ENCODED_WRITE ioctl. As with the encoded reads code, there's a test program for this at https://github.com/maharmstone/io_uring-encoded, and I'll get this worked into an fstest. How io_uring works is that it initially calls btrfs_uring_cmd with the IO_URING_F_NONBLOCK flag set, and if we return -EAGAIN it tries again in a kthread with the flag cleared. Ideally we'd honour this and call try_lock etc., but there's still a lot of work to be done to create non-blocking versions of all the functions in our write path. Instead, just validate the input in btrfs_uring_encoded_write() on the first pass and return -EAGAIN, with a view to properly optimizing the happy path later on. Signed-off-by: Mark Harmstone <maharmstone@fb.com> --- fs/btrfs/ioctl.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 116 insertions(+)