| Message ID | 20161129114707.2975-7-pbonzini@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Nov 29, 2016 at 12:47:03PM +0100, Paolo Bonzini wrote: > @@ -272,22 +275,32 @@ bool aio_prepare(AioContext *ctx) > bool aio_pending(AioContext *ctx) > { > AioHandler *node; > + bool result = false; > > - QLIST_FOREACH(node, &ctx->aio_handlers, node) { > + /* > + * We have to walk very carefully in case aio_set_fd_handler is > + * called while we're walking. > + */ > + qemu_lockcnt_inc(&ctx->list_lock); > + > + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { > int revents; > > revents = node->pfd.revents & node->pfd.events; > if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read && > aio_node_check(ctx, node->is_external)) { > - return true; > + result = true; > + break; > } > if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write && > aio_node_check(ctx, node->is_external)) { > - return true; > + result = true; > + break; > } > } > + qemu_lockcnt_dec(&ctx->list_lock); > > - return false; > + return result; > } > > bool aio_dispatch(AioContext *ctx) > @@ -308,13 +321,12 @@ bool aio_dispatch(AioContext *ctx) > * We have to walk very carefully in case aio_set_fd_handler is > * called while we're walking. > */ > - ctx->walking_handlers++; > + qemu_lockcnt_inc(&ctx->list_lock); > > - QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) { > + QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) { > int revents; > > - revents = node->pfd.revents & node->pfd.events; > - node->pfd.revents = 0; > + revents = atomic_xchg(&node->pfd.revents, 0) & node->pfd.events; Why is node->pfd.revents accessed with atomic_*() here and in aio_poll() but not in aio_pending()?
On 30/11/2016 14:31, Stefan Hajnoczi wrote: > On Tue, Nov 29, 2016 at 12:47:03PM +0100, Paolo Bonzini wrote: >> @@ -272,22 +275,32 @@ bool aio_prepare(AioContext *ctx) >> bool aio_pending(AioContext *ctx) >> { >> AioHandler *node; >> + bool result = false; >> >> - QLIST_FOREACH(node, &ctx->aio_handlers, node) { >> + /* >> + * We have to walk very carefully in case aio_set_fd_handler is >> + * called while we're walking. >> + */ >> + qemu_lockcnt_inc(&ctx->list_lock); >> + >> + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { >> int revents; >> >> revents = node->pfd.revents & node->pfd.events; >> if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read && >> aio_node_check(ctx, node->is_external)) { >> - return true; >> + result = true; >> + break; >> } >> if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write && >> aio_node_check(ctx, node->is_external)) { >> - return true; >> + result = true; >> + break; >> } >> } >> + qemu_lockcnt_dec(&ctx->list_lock); >> >> - return false; >> + return result; >> } >> >> bool aio_dispatch(AioContext *ctx) >> @@ -308,13 +321,12 @@ bool aio_dispatch(AioContext *ctx) >> * We have to walk very carefully in case aio_set_fd_handler is >> * called while we're walking. >> */ >> - ctx->walking_handlers++; >> + qemu_lockcnt_inc(&ctx->list_lock); >> >> - QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) { >> + QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) { >> int revents; >> >> - revents = node->pfd.revents & node->pfd.events; >> - node->pfd.revents = 0; >> + revents = atomic_xchg(&node->pfd.revents, 0) & node->pfd.events; > > Why is node->pfd.revents accessed with atomic_*() here and in aio_poll() > but not in aio_pending()? It could use atomic_read there, indeed. Paolo
On 30/11/2016 14:36, Paolo Bonzini wrote: > > > On 30/11/2016 14:31, Stefan Hajnoczi wrote: >> On Tue, Nov 29, 2016 at 12:47:03PM +0100, Paolo Bonzini wrote: >>> @@ -272,22 +275,32 @@ bool aio_prepare(AioContext *ctx) >>> bool aio_pending(AioContext *ctx) >>> { >>> AioHandler *node; >>> + bool result = false; >>> >>> - QLIST_FOREACH(node, &ctx->aio_handlers, node) { >>> + /* >>> + * We have to walk very carefully in case aio_set_fd_handler is >>> + * called while we're walking. >>> + */ >>> + qemu_lockcnt_inc(&ctx->list_lock); >>> + >>> + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { >>> int revents; >>> >>> revents = node->pfd.revents & node->pfd.events; >>> if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read && >>> aio_node_check(ctx, node->is_external)) { >>> - return true; >>> + result = true; >>> + break; >>> } >>> if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write && >>> aio_node_check(ctx, node->is_external)) { >>> - return true; >>> + result = true; >>> + break; >>> } >>> } >>> + qemu_lockcnt_dec(&ctx->list_lock); >>> >>> - return false; >>> + return result; >>> } >>> >>> bool aio_dispatch(AioContext *ctx) >>> @@ -308,13 +321,12 @@ bool aio_dispatch(AioContext *ctx) >>> * We have to walk very carefully in case aio_set_fd_handler is >>> * called while we're walking. >>> */ >>> - ctx->walking_handlers++; >>> + qemu_lockcnt_inc(&ctx->list_lock); >>> >>> - QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) { >>> + QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) { >>> int revents; >>> >>> - revents = node->pfd.revents & node->pfd.events; >>> - node->pfd.revents = 0; >>> + revents = atomic_xchg(&node->pfd.revents, 0) & node->pfd.events; >> >> Why is node->pfd.revents accessed with atomic_*() here and in aio_poll() >> but not in aio_pending()? > > It could use atomic_read there, indeed. Actually, thanks to the (already committed) patches that limit aio_poll to the I/O thread, these atomic accesses are not needed anymore. Paolo
diff --git a/aio-posix.c b/aio-posix.c index 93a50ad..c64d36d 100644 --- a/aio-posix.c +++ b/aio-posix.c @@ -16,7 +16,7 @@ #include "qemu/osdep.h" #include "qemu-common.h" #include "block/block.h" -#include "qemu/queue.h" +#include "qemu/rcu_queue.h" #include "qemu/sockets.h" #ifdef CONFIG_EPOLL_CREATE1 #include <sys/epoll.h> @@ -206,6 +206,8 @@ void aio_set_fd_handler(AioContext *ctx, bool is_new = false; bool deleted = false; + qemu_lockcnt_lock(&ctx->list_lock); + node = find_aio_handler(ctx, fd); /* Are we deleting the fd handler? */ @@ -217,7 +219,7 @@ void aio_set_fd_handler(AioContext *ctx, g_source_remove_poll(&ctx->source, &node->pfd); /* If the lock is held, just mark the node as deleted */ - if (ctx->walking_handlers) { + if (qemu_lockcnt_count(&ctx->list_lock)) { node->deleted = 1; node->pfd.revents = 0; } else { @@ -233,7 +235,7 @@ void aio_set_fd_handler(AioContext *ctx, /* Alloc and insert if it's not already there */ node = g_new0(AioHandler, 1); node->pfd.fd = fd; - QLIST_INSERT_HEAD(&ctx->aio_handlers, node, node); + QLIST_INSERT_HEAD_RCU(&ctx->aio_handlers, node, node); g_source_add_poll(&ctx->source, &node->pfd); is_new = true; @@ -249,6 +251,7 @@ void aio_set_fd_handler(AioContext *ctx, } aio_epoll_update(ctx, node, is_new); + qemu_lockcnt_unlock(&ctx->list_lock); aio_notify(ctx); if (deleted) { g_free(node); @@ -272,22 +275,32 @@ bool aio_prepare(AioContext *ctx) bool aio_pending(AioContext *ctx) { AioHandler *node; + bool result = false; - QLIST_FOREACH(node, &ctx->aio_handlers, node) { + /* + * We have to walk very carefully in case aio_set_fd_handler is + * called while we're walking. + */ + qemu_lockcnt_inc(&ctx->list_lock); + + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { int revents; revents = node->pfd.revents & node->pfd.events; if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read && aio_node_check(ctx, node->is_external)) { - return true; + result = true; + break; } if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write && aio_node_check(ctx, node->is_external)) { - return true; + result = true; + break; } } + qemu_lockcnt_dec(&ctx->list_lock); - return false; + return result; } bool aio_dispatch(AioContext *ctx) @@ -308,13 +321,12 @@ bool aio_dispatch(AioContext *ctx) * We have to walk very carefully in case aio_set_fd_handler is * called while we're walking. */ - ctx->walking_handlers++; + qemu_lockcnt_inc(&ctx->list_lock); - QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) { + QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) { int revents; - revents = node->pfd.revents & node->pfd.events; - node->pfd.revents = 0; + revents = atomic_xchg(&node->pfd.revents, 0) & node->pfd.events; if (!node->deleted && (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) && @@ -336,16 +348,15 @@ bool aio_dispatch(AioContext *ctx) } if (node->deleted) { - ctx->walking_handlers--; - if (!ctx->walking_handlers) { + if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) { QLIST_REMOVE(node, node); g_free(node); + qemu_lockcnt_inc_and_unlock(&ctx->list_lock); } - ctx->walking_handlers++; } } - ctx->walking_handlers--; + qemu_lockcnt_dec(&ctx->list_lock); /* Run our timers */ progress |= timerlistgroup_run_timers(&ctx->tlg); @@ -420,14 +431,12 @@ bool aio_poll(AioContext *ctx, bool blocking) atomic_add(&ctx->notify_me, 2); } - ctx->walking_handlers++; - + qemu_lockcnt_inc(&ctx->list_lock); assert(npfd == 0); /* fill pollfds */ - if (!aio_epoll_enabled(ctx)) { - QLIST_FOREACH(node, &ctx->aio_handlers, node) { + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { if (!node->deleted && node->pfd.events && aio_node_check(ctx, node->is_external)) { add_pollfd(node); @@ -464,12 +473,12 @@ bool aio_poll(AioContext *ctx, bool blocking) /* if we have any readable fds, dispatch event */ if (ret > 0) { for (i = 0; i < npfd; i++) { - nodes[i]->pfd.revents = pollfds[i].revents; + atomic_or(&nodes[i]->pfd.revents, pollfds[i].revents); } } npfd = 0; - ctx->walking_handlers--; + qemu_lockcnt_dec(&ctx->list_lock); /* Run dispatch even if there were no readable fds to run timers */ if (aio_dispatch(ctx)) {
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- aio-posix.c | 51 ++++++++++++++++++++++++++++++--------------------- 1 file changed, 30 insertions(+), 21 deletions(-)