On Tue, Jul 30, 2019 at 11:04:41PM +0530, Aarushi Mehta wrote: I'm concerned about file descriptor leaks. fd_array[] keeps file descriptors basically forever, even after the file is no longer in use by the rest of QEMU. There needs to be a call to unregister whenever a file is closed elsewhere in QEMU. For benchmarking and experimentation the current code is okay, but for production usage the leak must be prevented.
> +/** > + * luring_fd_register: > + * > + * Register and unregisters file descriptors, see luring_fd_lookup > + */ > +static int luring_fd_register(struct io_uring *ring, LuringFd *fd_reg, int > fd) > +{ > + int ret, nr; > + GHashTable *lookup = fd_reg->fd_lookup; > + nr = g_hash_table_size(lookup); > + > + /* Unregister */ > + if (!fd) { > + ret = io_uring_unregister_files(ring); > + g_hash_table_remove_all(lookup); Is it correct to clear the hash table be cleared if there was an error? > + return ret; > + } Please make unregistering all files a separate function. It's not necessary to overload this function since this is a completely separate operation. > + > + /* If adding new, API requires older registrations to be removed */ > + if (nr) { > + io_uring_unregister_files(ring); > + } > + > + fd_reg->fd_array = g_realloc_n(fd_reg->fd_array, nr + 1, sizeof(int)); > + fd_reg->fd_array[nr] = fd; > + fd_reg->fd_index = g_realloc_n(fd_reg->fd_index, nr + 1, sizeof(int)); > + fd_reg->fd_index[nr] = nr; > + > + g_hash_table_insert(lookup, &fd_reg->fd_array[nr], > &fd_reg->fd_index[nr]); fd_index[] is not necessary, you can cast nr to a gpointer instead to store the data directly inside GHashTable: g_hash_table_insert(lookup, &fd_reg->fd_array[nr], GINT_TO_POINTER(nr)); The hash table accesses can be made slightly more efficient by avoiding the pointer dereference for keys as well: g_hash_table_insert(lookup, GINT_TO_POINTER(fd), GINT_TO_POINTER(nr)); In this case fd_array[] is only used for the io_uring_register_files() call and nothing else. Remember to switch to g_direct_equal() and g_direct_hash() in g_hash_table_new_full() if you make the key a direct gpointer. > + trace_luring_fd_register(fd, nr); > + return io_uring_register_files(ring, fd_reg->fd_array, nr + 1); > +} > + > +/** > + * luring_fd_lookup: > + * > + * Used to lookup fd index in registered array at submission time > + * If the lookup table has not been created or the fd is not in the table, > + * the fd is registered. > + * > + * If registration errors, the hash is cleared and the fd used directly > + * > + * Unregistering is done at luring_detach_aio_context > + */ > +static int luring_fd_lookup(LuringState *s, int fd) > +{ > + int *index, ret; > + if (!s->fd_reg.fd_lookup) { > + s->fd_reg.fd_lookup = g_hash_table_new_full(g_int_hash, g_int_equal, > + g_free, g_free); fd_array[] and fd_index[] are allocated in single allocations for the entire array, therefore g_free(key) and g_free(value) on individual elements is undefined behavior and could crash the program. There should be no destroy function for them. Missing g_hash_table_unref() to free fd_lookup. > + luring_fd_register(&s->ring, &s->fd_reg, fd); > + } > + index = g_hash_table_lookup(s->fd_reg.fd_lookup, &fd); > + > + if (!index) { > + ret = luring_fd_register(&s->ring, &s->fd_reg, fd); > + if (ret < 0) { > + g_hash_table_remove_all(s->fd_reg.fd_lookup); Why is the hash table cleared and why are fd_array[]/fd_index[] left behind? > + return ret; > + } > + index = g_hash_table_lookup(s->fd_reg.fd_lookup, &fd); > + } > + return *index; > +} What are the concerns about in-flight requests and how are they addressed? For example, if a request is in-flight and another request wants to add a new fd then io_uring_unregister_files() and io_uring_register_files() are called while a request is still in-flight. How does the io_uring kernel code handle this?
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