Re: [PATCH 1/4] io_uring: track fixed files with a bitmap

[Jens Axboe <axboe@kernel.dk>]

On 5/9/22 7:26 AM, Hao Xu wrote:
> ? 2022/5/9 ??7:49, Jens Axboe ??:
>> In preparation for adding a basic allocator for direct descriptors,
>> add helpers that set/clear whether a file slot is used.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> ---
>>   fs/io_uring.c | 37 +++++++++++++++++++++++++++++++++++--
>>   1 file changed, 35 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index b6d491c9a25f..6eac6629e7d4 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -257,6 +257,7 @@ struct io_rsrc_put {
>>     struct io_file_table {
>>       struct io_fixed_file *files;
>> +    unsigned long *bitmap;
>>   };
>>     struct io_rsrc_node {
>> @@ -7573,6 +7574,7 @@ static inline struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
>>       /* mask in overlapping REQ_F and FFS bits */
>>       req->flags |= (file_ptr << REQ_F_SUPPORT_NOWAIT_BIT);
>>       io_req_set_rsrc_node(req, ctx, 0);
>> +    WARN_ON_ONCE(file && !test_bit(fd, ctx->file_table.bitmap));
>>   out:
>>       io_ring_submit_unlock(ctx, issue_flags);
>>       return file;
>> @@ -8639,13 +8641,35 @@ static bool io_alloc_file_tables(struct io_file_table *table, unsigned nr_files)
>>   {
>>       table->files = kvcalloc(nr_files, sizeof(table->files[0]),
>>                   GFP_KERNEL_ACCOUNT);
>> -    return !!table->files;
>> +    if (unlikely(!table->files))
>> +        return false;
>> +
>> +    table->bitmap = bitmap_zalloc(nr_files, GFP_KERNEL_ACCOUNT);
>> +    if (unlikely(!table->bitmap)) {
>> +        kvfree(table->files);
>> +        return false;
>> +    }
>> +
>> +    return true;
>>   }
>>     static void io_free_file_tables(struct io_file_table *table)
>>   {
>>       kvfree(table->files);
>> +    bitmap_free(table->bitmap);
>>       table->files = NULL;
>> +    table->bitmap = NULL;
>> +}
>> +
>> +static inline void io_file_bitmap_set(struct io_file_table *table, int bit)
>> +{
>> +    WARN_ON_ONCE(test_bit(bit, table->bitmap));
>> +    __set_bit(bit, table->bitmap);
>> +}
>> +
>> +static inline void io_file_bitmap_clear(struct io_file_table *table, int bit)
>> +{
>> +    __clear_bit(bit, table->bitmap);
>>   }
>>     static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
>> @@ -8660,6 +8684,7 @@ static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
>>               continue;
>>           if (io_fixed_file_slot(&ctx->file_table, i)->file_ptr & FFS_SCM)
>>               continue;
>> +        io_file_bitmap_clear(&ctx->file_table, i);
>>           fput(file);
>>       }
>>   #endif
>> @@ -9063,6 +9088,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
>>           }
>>           file_slot = io_fixed_file_slot(&ctx->file_table, i);
>>           io_fixed_file_set(file_slot, file);
>> +        io_file_bitmap_set(&ctx->file_table, i);
>>       }
>>         io_rsrc_node_switch(ctx, NULL);
>> @@ -9123,6 +9149,7 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>>           if (ret)
>>               goto err;
>>           file_slot->file_ptr = 0;
>> +        io_file_bitmap_clear(&ctx->file_table, slot_index);
>>           needs_switch = true;
>>       }
>>   @@ -9130,13 +9157,16 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>>       if (!ret) {
>>           *io_get_tag_slot(ctx->file_data, slot_index) = 0;
>>           io_fixed_file_set(file_slot, file);
>> +        io_file_bitmap_set(&ctx->file_table, slot_index);
> [1]
>>       }
>>   err:
>>       if (needs_switch)
>>           io_rsrc_node_switch(ctx, ctx->file_data);
>>       io_ring_submit_unlock(ctx, issue_flags);
>> -    if (ret)
>> +    if (ret) {
>> +        io_file_bitmap_clear(&ctx->file_table, slot_index);
> We don't need to clean it, since we get here only when we didn't
> run [1], which means we haven't set it.

Good point, agree. I'll drop that one.

-- 
Jens Axboe