From nobody Sat Nov 15 22:36:45 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 174722811923195.15389436650969; Wed, 14 May 2025 06:08:39 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uFBnw-00060j-Em; Wed, 14 May 2025 09:05:48 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uFBk6-0007ze-Cg; Wed, 14 May 2025 09:01:54 -0400 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uFBk3-0008KP-6k; Wed, 14 May 2025 09:01:50 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id B5DC9121B01; Wed, 14 May 2025 15:57:50 +0300 (MSK) Received: from think4mjt.tls.msk.ru (mjtthink.wg.tls.msk.ru [192.168.177.146]) by tsrv.corpit.ru (Postfix) with ESMTP id 5FF2020B86E; Wed, 14 May 2025 15:58:00 +0300 (MSK) From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Christian Schoenebeck , Greg Kurz , Michael Tokarev Subject: [Stable-9.2.4 34/34] 9pfs: fix FD leak and reduce latency of v9fs_reclaim_fd() Date: Wed, 14 May 2025 15:57:56 +0300 Message-Id: <20250514125758.92030-34-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.5 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1747228119916019000 Content-Type: text/plain; charset="utf-8" From: Christian Schoenebeck This patch fixes two different bugs in v9fs_reclaim_fd(): 1. Reduce latency: This function calls v9fs_co_close() and v9fs_co_closedir() in a loop. Each one of the calls adds two thread hops (between main thread and a fs driver background thread). Each thread hop adds latency, which sums up in function's loop to a significant duration. Reduce overall latency by open coding what v9fs_co_close() and v9fs_co_closedir() do, executing those and the loop itself altogether in only one background thread block, hence reducing the total amount of thread hops to only two. 2. Fix file descriptor leak: The existing code called v9fs_co_close() and v9fs_co_closedir() to close file descriptors. Both functions check right at the beginning if the 9p request was cancelled: if (v9fs_request_cancelled(pdu)) { return -EINTR; } So if client sent a 'Tflush' message, v9fs_co_close() / v9fs_co_closedir() returned without having closed the file descriptor and v9fs_reclaim_fd() subsequently freed the FID without its file descriptor being closed, hence leaking those file descriptors. This 2nd bug is fixed by this patch as well by open coding v9fs_co_close() and v9fs_co_closedir() inside of v9fs_reclaim_fd() and not performing the v9fs_request_cancelled(pdu) check there. Fixes: 7a46274529c ('hw/9pfs: Add file descriptor reclaim support') Fixes: bccacf6c792 ('hw/9pfs: Implement TFLUSH operation') Signed-off-by: Christian Schoenebeck Reviewed-by: Greg Kurz Message-Id: <5747469d3f039c53147e850b456943a1d4b5485c.1741339452.git.qemu_o= ss@crudebyte.com> (cherry picked from commit 89f7b4da7662ecc6840ffb0846045f03f9714bc6) Signed-off-by: Michael Tokarev diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c index f9aad55fdf..16207bdf22 100644 --- a/hw/9pfs/9p.c +++ b/hw/9pfs/9p.c @@ -434,6 +434,8 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu) V9fsFidState *f; GHashTableIter iter; gpointer fid; + int err; + int nclosed =3D 0; =20 /* prevent multiple coroutines running this function simultaniously */ if (s->reclaiming) { @@ -446,10 +448,10 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu) QSLIST_HEAD(, V9fsFidState) reclaim_list =3D QSLIST_HEAD_INITIALIZER(reclaim_list); =20 + /* Pick FIDs to be closed, collect them on reclaim_list. */ while (g_hash_table_iter_next(&iter, &fid, (gpointer *) &f)) { /* - * Unlink fids cannot be reclaimed. Check - * for them and skip them. Also skip fids + * Unlinked fids cannot be reclaimed, skip those, and also skip fi= ds * currently being operated on. */ if (f->ref || f->flags & FID_NON_RECLAIMABLE) { @@ -499,17 +501,26 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu) } } /* - * Now close the fid in reclaim list. Free them if they - * are already clunked. + * Close the picked FIDs altogether on a background I/O driver thread.= Do + * this all at once to keep latency (i.e. amount of thread hops betwee= n main + * thread <-> fs driver background thread) as low as possible. */ + v9fs_co_run_in_worker({ + QSLIST_FOREACH(f, &reclaim_list, reclaim_next) { + err =3D (f->fid_type =3D=3D P9_FID_DIR) ? + s->ops->closedir(&s->ctx, &f->fs_reclaim) : + s->ops->close(&s->ctx, &f->fs_reclaim); + if (!err) { + /* total_open_fd must only be mutated on main thread */ + nclosed++; + } + } + }); + total_open_fd -=3D nclosed; + /* Free the closed FIDs. */ while (!QSLIST_EMPTY(&reclaim_list)) { f =3D QSLIST_FIRST(&reclaim_list); QSLIST_REMOVE(&reclaim_list, f, V9fsFidState, reclaim_next); - if (f->fid_type =3D=3D P9_FID_FILE) { - v9fs_co_close(pdu, &f->fs_reclaim); - } else if (f->fid_type =3D=3D P9_FID_DIR) { - v9fs_co_closedir(pdu, &f->fs_reclaim); - } /* * Now drop the fid reference, free it * if clunked. --=20 2.39.5