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  1. 09 1月, 2019 9 次提交
  3. 07 1月, 2019 1 次提交
    • L
      Change mincore() to count "mapped" pages rather than "cached" pages · 574823bf
      由 Linus Torvalds 提交于 
      The semantics of what "in core" means for the mincore() system call are
somewhat unclear, but Linux has always (since 2.3.52, which is when
mincore() was initially done) treated it as "page is available in page
cache" rather than "page is mapped in the mapping".

The problem with that traditional semantic is that it exposes a lot of
system cache state that it really probably shouldn't, and that users
shouldn't really even care about.

So let's try to avoid that information leak by simply changing the
semantics to be that mincore() counts actual mapped pages, not pages
that might be cheaply mapped if they were faulted (note the "might be"
part of the old semantics: being in the cache doesn't actually guarantee
that you can access them without IO anyway, since things like network
filesystems may have to revalidate the cache before use).

In many ways the old semantics were somewhat insane even aside from the
information leak issue.  From the very beginning (and that beginning is
a long time ago: 2.3.52 was released in March 2000, I think), the code
had a comment saying

  Later we can get more picky about what "in core" means precisely.

and this is that "later".  Admittedly it is much later than is really
comfortable.

NOTE! This is a real semantic change, and it is for example known to
change the output of "fincore", since that program literally does a
mmmap without populating it, and then doing "mincore()" on that mapping
that doesn't actually have any pages in it.

I'm hoping that nobody actually has any workflow that cares, and the
info leak is real.

We may have to do something different if it turns out that people have
valid reasons to want the old semantics, and if we can limit the
information leak sanely.

Cc: Kevin Easton <kevin@guarana.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Masatake YAMATO <yamato@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      574823bf
  5. 05 1月, 2019 5 次提交
  7. 04 1月, 2019 1 次提交
    • L
      Remove 'type' argument from access_ok() function · 96d4f267
      由 Linus Torvalds 提交于 
      Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument
of the user address range verification function since we got rid of the
old racy i386-only code to walk page tables by hand.

It existed because the original 80386 would not honor the write protect
bit when in kernel mode, so you had to do COW by hand before doing any
user access.  But we haven't supported that in a long time, and these
days the 'type' argument is a purely historical artifact.

A discussion about extending 'user_access_begin()' to do the range
checking resulted this patch, because there is no way we're going to
move the old VERIFY_xyz interface to that model.  And it's best done at
the end of the merge window when I've done most of my merges, so let's
just get this done once and for all.

This patch was mostly done with a sed-script, with manual fix-ups for
the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form.

There were a couple of notable cases:

 - csky still had the old "verify_area()" name as an alias.

 - the iter_iov code had magical hardcoded knowledge of the actual
   values of VERIFY_{READ,WRITE} (not that they mattered, since nothing
   really used it)

 - microblaze used the type argument for a debug printout

but other than those oddities this should be a total no-op patch.

I tried to fix up all architectures, did fairly extensive grepping for
access_ok() uses, and the changes are trivial, but I may have missed
something.  Any missed conversion should be trivially fixable, though.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      96d4f267
  9. 03 1月, 2019 1 次提交
    • L
      block: don't use un-ordered __set_current_state(TASK_UNINTERRUPTIBLE) · 1ac5cd49
      由 Linus Torvalds 提交于 
      This mostly reverts commit 849a3700 ("block: avoid ordered task
state change for polled IO").  It was wrongly claiming that the ordering
wasn't necessary.  The memory barrier _is_ necessary.

If something is truly polling and not going to sleep, it's the whole
state setting that is unnecessary, not the memory barrier.  Whenever you
set your state to a sleeping state, you absolutely need the memory
barrier.

Note that sometimes the memory barrier can be elsewhere.  For example,
the ordering might be provided by an external lock, or by setting the
process state to sleeping before adding yourself to the wait queue list
that is used for waking up (where the wait queue lock itself will
guarantee that any wakeup will correctly see the sleeping state).

But none of those cases were true here.

NOTE! Some of the polling paths may indeed be able to drop the state
setting entirely, at which point the memory barrier also goes away.

(Also note that this doesn't revert the TASK_RUNNING cases: there is no
race between a wakeup and setting the process state to TASK_RUNNING,
since the end result doesn't depend on ordering).

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      1ac5cd49
  11. 29 12月, 2018 23 次提交