On Mon, Jan 09, 2023 at 09:31:00AM -0500, Jeff Layton wrote: > 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 actually think we may have the opposite problem; that for some of these scenarios, we never mark the error as seen. ie we always end up calling errseq_check() and never errseq_check_and_advance(). So every time we write something, it'll remind us that we have an error.
