| Message ID | 1318538102-6982-1-git-send-email-harsh@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On 10/13/2011 10:35 PM, Harsh Prateek Bora wrote: > > +#define QLIST_INSERT_HEAD_RCU(head, elm, field) do { \ > + (elm)->field.le_prev =&(head)->lh_first; \ > + smp_wmb(); \ > + if (((elm)->field.le_next = (head)->lh_first) != NULL) \ > + (head)->lh_first->field.le_prev =&(elm)->field.le_next;\ > + smp_wmb(); \ > + (head)->lh_first = (elm); \ > + smp_wmb(); \ > +} while (/* CONSTCOND*/0) Actually, looking more at it it should be more like (elm)->field.le_prev =&(head)->lh_first; (elm)->field.le_next = (head)->lh_first; smb_wmb(); /* fill elm before linking it */ if ((head)->lh_first != NULL) (head)->lh_first->field.le_prev =&(elm)->field.le_next; (head)->lh_first = (elm); smp_wmb(); ... which even saves a memory barrier. Paolo
diff --git a/qemu-queue.h b/qemu-queue.h index 1d07745..57234f8 100644 --- a/qemu-queue.h +++ b/qemu-queue.h @@ -76,6 +76,8 @@ * For details on the use of these macros, see the queue(3) manual page. */ +#include "qemu-barrier.h" /* for smp_wmb() */ + /* * List definitions. */ @@ -122,6 +124,16 @@ struct { \ (elm)->field.le_prev = &(head)->lh_first; \ } while (/*CONSTCOND*/0) +#define QLIST_INSERT_HEAD_RCU(head, elm, field) do { \ + (elm)->field.le_prev = &(head)->lh_first; \ + smp_wmb(); \ + if (((elm)->field.le_next = (head)->lh_first) != NULL) \ + (head)->lh_first->field.le_prev = &(elm)->field.le_next;\ + smp_wmb(); \ + (head)->lh_first = (elm); \ + smp_wmb(); \ +} while (/* CONSTCOND*/0) + #define QLIST_REMOVE(elm, field) do { \ if ((elm)->field.le_next != NULL) \ (elm)->field.le_next->field.le_prev = \ diff --git a/qemu-thread.h b/qemu-thread.h index 0a73d50..e008b60 100644 --- a/qemu-thread.h +++ b/qemu-thread.h @@ -19,6 +19,9 @@ void qemu_mutex_lock(QemuMutex *mutex); int qemu_mutex_trylock(QemuMutex *mutex); void qemu_mutex_unlock(QemuMutex *mutex); +#define rcu_read_lock() do { } while (0) +#define rcu_read_unlock() do { } while (0) + void qemu_cond_init(QemuCond *cond); void qemu_cond_destroy(QemuCond *cond);
SynthFS needs a QLIST_INSERT_HEAD_RCU to make sure list instructions are not re-ordered and therefore avoiding a crash. There may be parallel readers which should be allowed for lock-free access and this variant allows us to get rid of rwlocks used by readers. SynthFS is a special case where we dont really need full RCU capabilities as it doesnt allow list entry deletion but concurrent readers/writers and instruction re-ordering should not result in a crash. Also, once the real rcu is available, dummy rcu macro definitions will go away and the code will still work as expected. This patchwork is based on inputs from Paolo Bonzini. Signed-off-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com> --- qemu-queue.h | 12 ++++++++++++ qemu-thread.h | 3 +++ 2 files changed, 15 insertions(+), 0 deletions(-)