On 2/17/20 10:46 AM, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" <[email protected]> > > By putting the 'have we reached the end of the page' condition at the end > of the loop instead of the beginning, we can remove the 'submit the last > page' code from iomap_readpages(). Also check that iomap_readpage_actor() > didn't return 0, which would lead to an endless loop.
Also added a new WARN_ON() and BUG(), although I'm wondering about the BUG below... > > Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> > --- > fs/iomap/buffered-io.c | 25 ++++++++++++------------- > 1 file changed, 12 insertions(+), 13 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index cb3511eb152a..44303f370b2d 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -400,15 +400,9 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, > loff_t length, > void *data, struct iomap *iomap, struct iomap *srcmap) > { > struct iomap_readpage_ctx *ctx = data; > - loff_t done, ret; > + loff_t ret, done = 0; > > - for (done = 0; done < length; done += ret) { nit: this "for" loop was perfect just the way it was. :) I'd vote here for reverting the change to a "while" loop. Because with this change, now the code has to separately initialize "done", separately increment "done", and the beauty of a for loop is that the loop init and control is all clearly in one place. For things that follow that model (as in this case!), that's a Good Thing. And I don't see any technical reason (even in the following patch) that requires this change. > - if (ctx->cur_page && offset_in_page(pos + done) == 0) { > - if (!ctx->cur_page_in_bio) > - unlock_page(ctx->cur_page); > - put_page(ctx->cur_page); > - ctx->cur_page = NULL; > - } > + while (done < length) { > if (!ctx->cur_page) { > ctx->cur_page = iomap_next_page(inode, ctx->pages, > pos, length, &done); > @@ -418,6 +412,15 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, > loff_t length, > } > ret = iomap_readpage_actor(inode, pos + done, length - done, > ctx, iomap, srcmap); > + if (WARN_ON(ret == 0)) > + break; > + done += ret; > + if (offset_in_page(pos + done) == 0) { > + if (!ctx->cur_page_in_bio) > + unlock_page(ctx->cur_page); > + put_page(ctx->cur_page); > + ctx->cur_page = NULL; > + } > } > > return done; > @@ -451,11 +454,7 @@ iomap_readpages(struct address_space *mapping, struct > list_head *pages, > done: > if (ctx.bio) > submit_bio(ctx.bio); > - if (ctx.cur_page) { > - if (!ctx.cur_page_in_bio) > - unlock_page(ctx.cur_page); > - put_page(ctx.cur_page); > - } > + BUG_ON(ctx.cur_page); Is a full BUG_ON() definitely called for here? Seems like a WARN might suffice... > > /* > * Check that we didn't lose a page due to the arcance calling > thanks, -- John Hubbard NVIDIA
