From: Christian Brauner > Sent: 26 July 2023 09:37 ... > Yes, and to summarize which I tried in my description for the commit. > The getdents support patchset would have introduced a bug because the > patchset copied the fdget_pos() file_count(file) > 1 optimization into > io_uring. > > That works fine as long as the original file descriptor used to register > the fixed file is kept. The locking will work correctly as > file_count(file) > 1 and no races are possible neither via getdent calls > using the original file descriptor nor via io_uring using the fixed file > or even mixing both. > > But as soon as the original file descriptor is closed the f_count for > the file drops back to 1 but continues to be usable from io_uring via > the fixed file. Now the optimization that the patchset wanted to copy > over would cause bugs as multiple racing getdent requests would be > possible using the fixed file. Could the io_uring code grab two references? That would stop the optimisation without affecting any normal code paths? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
