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  1. 03 Aug, 2011 3 commits
    • Huang Ying's avatar
      lib, Make gen_pool memory allocator lockless · 7f184275
      Huang Ying authored 
      This version of the gen_pool memory allocator supports lockless
operation.

This makes it safe to use in NMI handlers and other special
unblockable contexts that could otherwise deadlock on locks.  This is
implemented by using atomic operations and retries on any conflicts.
The disadvantage is that there may be livelocks in extreme cases.  For
better scalability, one gen_pool allocator can be used for each CPU.

The lockless operation only works if there is enough memory available.
If new memory is added to the pool a lock has to be still taken.  So
any user relying on locklessness has to ensure that sufficient memory
is preallocated.

The basic atomic operation of this allocator is cmpxchg on long.  On
architectures that don't have NMI-safe cmpxchg implementation, the
allocator can NOT be used in NMI handler.  So code uses the allocator
in NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
Reviewed-by: default avatarAndi Kleen <ak@linux.intel.com>
Reviewed-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
      7f184275
    • Huang Ying's avatar
      lib, Add lock-less NULL terminated single list · f49f23ab
      Huang Ying authored 
      Cmpxchg is used to implement adding new entry to the list, deleting
all entries from the list, deleting first entry of the list and some
other operations.

Because this is a single list, so the tail can not be accessed in O(1).

If there are multiple producers and multiple consumers, llist_add can
be used in producers and llist_del_all can be used in consumers.  They
can work simultaneously without lock.  But llist_del_first can not be
used here.  Because llist_del_first depends on list->first->next does
not changed if list->first is not changed during its operation, but
llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
llist_add) sequence in another consumer may violate that.

If there are multiple producers and one consumer, llist_add can be
used in producers and llist_del_all or llist_del_first can be used in
the consumer.

This can be summarized as follow:

           |   add    | del_first |  del_all
 add       |    -     |     -     |     -
 del_first |          |     L     |     L
 del_all   |          |           |     -

Where "-" stands for no lock is needed, while "L" stands for lock is
needed.

The list entries deleted via llist_del_all can be traversed with
traversing function such as llist_for_each etc.  But the list entries
can not be traversed safely before deleted from the list.  The order
of deleted entries is from the newest to the oldest added one.  If you
want to traverse from the oldest to the newest, you must reverse the
order by yourself before traversing.

The basic atomic operation of this list is cmpxchg on long.  On
architectures that don't have NMI-safe cmpxchg implementation, the
list can NOT be used in NMI handler.  So code uses the list in NMI
handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
Reviewed-by: default avatarAndi Kleen <ak@linux.intel.com>
Reviewed-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
      f49f23ab
    • Huang Ying's avatar
      Add Kconfig option ARCH_HAVE_NMI_SAFE_CMPXCHG · df013ffb
      Huang Ying authored 
      cmpxchg() is widely used by lockless code, including NMI-safe lockless
code.  But on some architectures, the cmpxchg() implementation is not
NMI-safe, on these architectures the lockless code may need a
spin_trylock_irqsave() based implementation.

This patch adds a Kconfig option: ARCH_HAVE_NMI_SAFE_CMPXCHG, so that
NMI-safe lockless code can depend on it or provide different
implementation according to it.

On many architectures, cmpxchg is only NMI-safe for several specific
operand sizes. So, ARCH_HAVE_NMI_SAFE_CMPXCHG define in this patch
only guarantees cmpxchg is NMI-safe for sizeof(unsigned long).
Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
Acked-by: default avatarMike Frysinger <vapier@gentoo.org>
Acked-by: default avatarPaul Mundt <lethal@linux-sh.org>
Acked-by: default avatarHans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Acked-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: default avatarChris Metcalf <cmetcalf@tilera.com>
Acked-by: default avatarRichard Henderson <rth@twiddle.net>
CC: Mikael Starvik <starvik@axis.com>
Acked-by: default avatarDavid Howells <dhowells@redhat.com>
CC: Yoshinori Sato <ysato@users.sourceforge.jp>
CC: Tony Luck <tony.luck@intel.com>
CC: Hirokazu Takata <takata@linux-m32r.org>
CC: Geert Uytterhoeven <geert@linux-m68k.org>
CC: Michal Simek <monstr@monstr.eu>
Acked-by: default avatarRalf Baechle <ralf@linux-mips.org>
CC: Kyle McMartin <kyle@mcmartin.ca>
CC: Martin Schwidefsky <schwidefsky@de.ibm.com>
CC: Chen Liqin <liqin.chen@sunplusct.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Ingo Molnar <mingo@redhat.com>
CC: Chris Zankel <chris@zankel.net>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
      df013ffb
  3. 14 Jul, 2011 10 commits
  5. 12 Jul, 2011 8 commits
  7. 11 Jul, 2011 19 commits
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