On Mon, 2023-01-09 at 14:02 +0000, Matthew Wilcox wrote: > On Mon, Jan 09, 2023 at 08:48:49AM -0500, Jeff Layton wrote: > > On Mon, 2023-01-09 at 05:18 +0000, Matthew Wilcox (Oracle) wrote: > > > Convert both callers to use the "new" errseq infrastructure. > > > > I looked at making this sort of change across the board alongside the > > original wb_err patches, but I backed off at the time. > > > > With the above patch, this function will no longer report a writeback > > error that occurs before the sample. Given that writeback can happen at > > any time, that seemed like it might be an undesirable change, and I > > didn't follow through. > > > > It is true that the existing flag-based code may miss errors too, if > > multiple tasks are test_and_clear'ing the bits, but I think the above is > > even more likely to happen, esp. under memory pressure. > > > > To do this right, we probably need to look at these callers and have > > them track a long-term errseq_t "since" value before they ever dirty the > > pages, and then continually check-and-advance vs. that. > > > > For instance, the main caller of the above function is jbd2. Would it be > > reasonable to add in a new errseq_t value to the jnode for tracking > > errors? > > Doesn't b4678df184b3 address this problem? If nobody has seen the > error, we return 0 instead of the current value of wb_err, ensuring > that somebody always sees the error. > I was originally thinking no, but now I think you're correct. We do initialize the "since" value to 0 if an error has never been seen, so that (sort of) emulates the behavior of the existing AS_EIO/AS_ENOSPC flags. It's still not quite as reliable as plumbing a "since" value through all of the callers (particularly in the case where there are multiple waiters), but maybe it's good enough here. I'll look over the rest of the set. Thanks, -- Jeff Layton <jlayton@xxxxxxxxxx>
