On 1/8/21 4:39 PM, Martin Raiber wrote: > Hi, > > I have a gnarly issue with io_uring and fixed buffers (fixed > read/write). It seems the contents of those buffers contain old data in > some rare cases under memory pressure after a read/during a write. > > Specifically I use io_uring with fuse and to confirm this is not some > user space issue let fuse print the unique id it adds to each request. > Fuse adds this request data to a pipe, and when the pipe buffer is later > copied to the io_uring fixed buffer it has the id of a fuse request > returned earlier using the same buffer while returning the size of the > new request. Or I set the unique id in the buffer, write it to fuse (via > writing to a pipe, then splicing) and then fuse returns with e.g. > ENOENT, because the unique id is not correct because in kernel it reads > the id of the previous, already completed, request using this buffer. > > To make reproducing this faster running memtester (which mlocks a > configurable amount of memory) with a large amount of user memory every > 30s helps. So it has something to do with swapping? It seems to not > occur if no swap space is active. Problem occurs without warning when > the kernel is build with KASAN and slab debugging. > > If I don't use the _FIXED opcodes (which is easy to do), the problem > does not occur. > > Problem occurs with 5.9.16 and 5.10.5. Can you mention more about what kind of IO you are doing, I'm assuming it's O_DIRECT? I'll see if I can reproduce this. -- Jens Axboe
