Skip to content
  1. Apr 16, 2019
  3. Apr 15, 2019
  5. Apr 13, 2019
    • David S. Miller's avatar
      Merge branch 'rhashtable-bit-locking-m68k' · 5fa7d3f9
      David S. Miller authored 
      

NeilBrown says:

====================
Fix rhashtable bit-locking for m68k

As reported by Guenter Roeck, the new rhashtable bit-locking
doesn't work on m68k as it only requires 2-byte alignment, so BIT(1)
is addresses is not unused.

We current use BIT(0) to identify a NULLS marker, but that is only
needed in ->next pointers.  The bucket head does not need a NULLS
marker, so the lsb there can be used for locking.

the first 4 patches make some small improvements and re-arrange some
code.  The final patch converts to using only BIT(0) for these two
different special purposes.

I had previously suggested dropping the series until I fix it.  Given
that this was fairly easy, I retract that I think it best simply to
add these patches to fix the code.
====================

Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      5fa7d3f9
    • NeilBrown's avatar
      rhashtable: use BIT(0) for locking. · ca0b709d
      NeilBrown authored 
      As reported by Guenter Roeck, the new bit-locking using
BIT(1) doesn't work on the m68k architecture.  m68k only requires
2-byte alignment for words and longwords, so there is only one
unused bit in pointers to structs - We current use two, one for the
NULLS marker at the end of the linked list, and one for the bit-lock
in the head of the list.

The two uses don't need to conflict as we never need the head of the
list to be a NULLS marker - the marker is only needed to check if an
object has moved to a different table, and the bucket head cannot
move.  The NULLS marker is only needed in a ->next pointer.

As we already have different types for the bucket head pointer (struct
rhash_lock_head) and the ->next pointers (struct rhash_head), it is
fairly easy to treat the lsb differently in each.

So: Initialize buckets heads to NULL, and use the lsb for locking.
When loading the pointer from the bucket head, if it is NULL (ignoring
the lock big), report as being the expected NULLS marker.
When storing a value into a bucket head, if it is a NULLS marker,
store NULL instead.

And convert all places that used bit 1 for locking, to use bit 0.

Fixes: 8f0db018

 ("rhashtable: use bit_spin_locks to protect hash bucket.")
Reported-by: default avatarGuenter Roeck <linux@roeck-us.net>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      ca0b709d
    • NeilBrown's avatar
      rhashtable: replace rht_ptr_locked() with rht_assign_locked() · f4712b46
      NeilBrown authored 
      

The only times rht_ptr_locked() is used, it is to store a new
value in a bucket-head.  This is the only time it makes sense
to use it too.  So replace it by a function which does the
whole task:  Sets the lock bit and assigns to a bucket head.

Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      f4712b46
    • NeilBrown's avatar
      rhashtable: move dereference inside rht_ptr() · adc6a3ab
      NeilBrown authored 
      

Rather than dereferencing a pointer to a bucket and then passing the
result to rht_ptr(), we now pass in the pointer and do the dereference
in rht_ptr().

This requires that we pass in the tbl and hash as well to support RCU
checks, and means that the various rht_for_each functions can expect a
pointer that can be dereferenced without further care.

There are two places where we dereference a bucket pointer
where there is no testable protection - in each case we know
that we much have exclusive access without having taken a lock.
The previous code used rht_dereference() to pretend that holding
the mutex provided protects, but holding the mutex never provides
protection for accessing buckets.

So instead introduce rht_ptr_exclusive() that can be used when
there is known to be exclusive access without holding any locks.

Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      adc6a3ab
    • NeilBrown's avatar
      rhashtable: reorder some inline functions and macros. · c5783311
      NeilBrown authored 
      

This patch only moves some code around, it doesn't
change the code at all.
A subsequent patch will benefit from this as it needs
to add calls to functions which are now defined before the
call-site, but weren't before.

Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      c5783311