[ add Willy and Jan ] On Sun, Dec 9, 2018 at 10:02 AM Linus Torvalds <torva...@linux-foundation.org> wrote: > > On Sat, Dec 8, 2018 at 10:26 PM Williams, Dan J > <dan.j.willi...@intel.com> wrote: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm > > tags/dax-fixes-4.20-rc6 > > What's going on with the odd non-exclusive exclusive wait? > > prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE); > ... > /* > * Entry lock waits are exclusive. Wake up the next waiter since > * we aren't sure we will acquire the entry lock and thus wake > * the next waiter up on unlock. > */ > if (waitqueue_active(wq)) > __wake_up(wq, TASK_NORMAL, 1, &ewait.key); > > that seems to make little or no sense. > > Why isn't that prepare_to_wait_exclusive() just a regular > prepare_to_wait(), and then the whole "let's wake up anybody else" can > be removed? > > I've pulled it, but am awaiting explanation of what looks like some > pretty crazy code. I *suspect* it's a copy-and-paste situation where > you took the exclusive wait from somewhere else.
Yes, I believe that's true. In the other instances of waiting for an entry to be in unlocked there is a guarantee that the waiter will attain the lock and perform an unlock + wakeup. In the dax_lock_page() path there is the possibility that the inode dies before the lock is attained and a subsequent unlock sequence is not guaranteed. So, I believe the intent, Willy correct me if I am wrong, was to keep all waits "exclusive" for some sense of symmetry, but this one can and should be a non-exclusive wait. I can send a cleanup, do you want one immediately, or is post -rc6 ok? _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm
