On Mon, Sep 04, 2023 at 08:27:15AM +1000, Dave Chinner wrote: > It already is (sysrq-t), but I'm not sure that will help - if it is > a leaked unlock then nothing will show up at all. Unlikely; grep and you'll see - very few callers, and for all of them there's an fdput_pos() downstream of any fdget_pos() that had picked non-NULL file reference. In theory, it's not impossible that something had stripped FDPUT_POS_UNLOCK from the flags, but that's basically "something might've corrupted the local variables" scenario. There are 12 functions total where we might be calling fdget_pos() and all of them are pretty small (1 in alpha osf_sys.c, 6 in read_write.c and 5 in readdir.c); none of those takes an address of struct fd, none of them has assignments to it after fdget_pos() and the only accesses to its members are those to fd.file - all fetches. Control flow is also easy to check - they are all short. IMO it's much more likely that we'll find something like thread A: grabs some fs lock gets stuck on something thread B: write() finds file grabs ->f_pos_lock calls into filesystem blocks on fs lock held by A thread C: read()/write()/lseek() on the same file blocks on ->f_pos_lock
