That sounds like a reasonable approach to me! Thanx, Paul On Tue, Sep 27, 2022 at 03:12:51PM -0400, Elad Lahav wrote: > I'll try to come up with a patch that combines 1 and 2. So keep the > qsort() example, but then add something along the lines of: > > "If you are not convinced that qsort requires locking in the library, > consider the following example..." > > and then > > "Note the dangerous situation as the library releases its locks prior > to invoking the user's callback function..." > > --Elad > > On Tue, 27 Sept 2022 at 15:06, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > On Mon, Sep 26, 2022 at 09:48:33PM -0400, Elad Lahav wrote: > > > This started out as a longer email, but it looks like at least two of > > > the problems I spotted were already fixed in the latest version. > > > > > > 1. I think the recommendation to release all locks before invoking a > > > user-supplied function should come with a BIG FLASHING WARNING SIGN > > > (or the PDF equivalent). Whenever I review code that releases and > > > re-acquires a lock I look for the faulty assumptions it makes about > > > state being preserved from before the lock was released. 9 out of 10 > > > times I find a bug. > > > > Good point! > > > > Left to myself, I would add another infamous Quick Quiz. But would > > you like to send a patch proposing something? > > > > > 2. qsort() may not be the best example to use in this section, as, > > > even assuming there is some version of it that requires locks, the > > > reader may fail to see any problems. While I'm no fan of nftw(), it > > > may be easier to see why you would need a lock in the library (to > > > prevent changes to the directory), as well as why releasing and > > > re-acquiring the lock can be dangerous (the iterator can become > > > invalid). > > > > This does sound better than qsort, so if no one has a better suggestion, I > > would be tempted to go with that. In the absence of a better suggestion, > > would you be willing to supply some sample code, preferably buildable > > and executable? > > > > > 3. Page 106, first paragraph: "an pointer" should be "a pointer". > > > > This one was easy, so I applied it with your Reported-by. Good eyes, > > by the way, and thank you! > > > > Thanx, Paul
