[0/2] Killable synchronous BIO submission

Message

Matthew Wilcox (Oracle) Oct. 16, 2020, 4:14 p.m. UTC

It would be nice to be able to report the actual errors from block devices
instead of the default -EIO.  In order to do that, we need to execute the
BIO synchronously as the only way to get the error back to the caller is
by returning it from readpage() -- we can't store it in the struct page.

But we need to be able to respond to a fatal signal, as we do today with
lock_page_killable().  This turns out to be quite hard.  The solution
I settled on is that the caller must pass in an alternate end_io to be
called asynchronously if a fatal signal arrives.

I believe the synchronize_rcu() call to be sufficient to ensure that the
old bi_end_io() will not be called.  If there are callers of bi_end_io()
from BH-enabled regions, it may not be!  Perhaps we could put a warning
in bio_endio() to make sure that's true?

Matthew Wilcox (Oracle) (2):
  block: Add submit_bio_killable
  fs: Make mpage_readpage synchronous

 block/bio.c                | 87 +++++++++++++++++++++++++++++---------
 fs/mpage.c                 | 25 +++++++++--
 include/linux/bio.h        |  1 +
 include/linux/completion.h |  1 +
 kernel/sched/completion.c  |  9 ++--
 5 files changed, 97 insertions(+), 26 deletions(-)