Re: [Qemu-block] [PATCH 06/10] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock
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, >aio_handlers, node) { >>> +/* >>> + * We have to walk very carefully in case aio_set_fd_handler is >>> + * called while we're walking. >>> + */ >>> +qemu_lockcnt_inc(>list_lock); >>> + >>> +QLIST_FOREACH_RCU(node, >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(>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(>list_lock); >>> >>> -QLIST_FOREACH_SAFE(node, >aio_handlers, node, tmp) { >>> +QLIST_FOREACH_SAFE_RCU(node, >aio_handlers, node, tmp) { >>> int revents; >>> >>> -revents = node->pfd.revents & node->pfd.events; >>> -node->pfd.revents = 0; >>> +revents = atomic_xchg(>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
Re: [Qemu-block] [PATCH 06/10] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock
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, >aio_handlers, node) { >> +/* >> + * We have to walk very carefully in case aio_set_fd_handler is >> + * called while we're walking. >> + */ >> +qemu_lockcnt_inc(>list_lock); >> + >> +QLIST_FOREACH_RCU(node, >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(>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(>list_lock); >> >> -QLIST_FOREACH_SAFE(node, >aio_handlers, node, tmp) { >> +QLIST_FOREACH_SAFE_RCU(node, >aio_handlers, node, tmp) { >> int revents; >> >> -revents = node->pfd.revents & node->pfd.events; >> -node->pfd.revents = 0; >> +revents = atomic_xchg(>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 signature.asc Description: OpenPGP digital signature
Re: [Qemu-block] [PATCH 06/10] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock
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, >aio_handlers, node) { > +/* > + * We have to walk very carefully in case aio_set_fd_handler is > + * called while we're walking. > + */ > +qemu_lockcnt_inc(>list_lock); > + > +QLIST_FOREACH_RCU(node, >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(>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(>list_lock); > > -QLIST_FOREACH_SAFE(node, >aio_handlers, node, tmp) { > +QLIST_FOREACH_SAFE_RCU(node, >aio_handlers, node, tmp) { > int revents; > > -revents = node->pfd.revents & node->pfd.events; > -node->pfd.revents = 0; > +revents = atomic_xchg(>pfd.revents, 0) & node->pfd.events; Why is node->pfd.revents accessed with atomic_*() here and in aio_poll() but not in aio_pending()? signature.asc Description: PGP signature