On Tue, Sep 20, 2022 at 01:56:25PM -0400, Mikulas Patocka wrote: > This patch extends the rcu regions, so that lookup followed by a read or > write of a page is done inside rcu read lock. This si be needed for the > following patch that enables discard. > > Note that we also replace "BUG_ON(!page);" with "if (page) ..." in > copy_to_brd - the page may be NULL if write races with discard. In this > situation, the result is undefined, so we can actually skip the write > operation at all. > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > --- > drivers/block/brd.c | 59 +++++++++++++++++++++++----------------------------- > 1 file changed, 27 insertions(+), 32 deletions(-) > > Index: linux-2.6/drivers/block/brd.c > =================================================================== > --- linux-2.6.orig/drivers/block/brd.c > +++ linux-2.6/drivers/block/brd.c > @@ -50,31 +50,12 @@ struct brd_device { > > /* > * Look up and return a brd's page for a given sector. > + * This must be called with the rcu lock held. > */ > static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector) > { > + pgoff_t idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */ > + return radix_tree_lookup(&brd->brd_pages, idx); > } This is still missing the rcu_read_lock_held() assertation if you want to keep it as separate function. > + rcu_read_lock(); > + page = brd_lookup_page(brd, sector); > + if (page) { > + dst = kmap_atomic(page); > + memcpy(dst + offset, src, copy); > + kunmap_atomic(dst); > + } > + rcu_read_unlock(); How is the null check going to work here? Simply not copying data is no exactly the expected result. This is why I think we need the higher level rework I suggested last time where we have a helper that always gives you page (or maybe an error) by moving the insert so that it also does the actual final lookup. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel