From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D105DCA9EAF for ; Fri, 25 Oct 2019 01:23:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A617621D7B for ; Fri, 25 Oct 2019 01:23:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388830AbfJYBXr (ORCPT ); Thu, 24 Oct 2019 21:23:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48212 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388701AbfJYBXr (ORCPT ); Thu, 24 Oct 2019 21:23:47 -0400 Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 606DAC049E10 for ; Fri, 25 Oct 2019 01:23:46 +0000 (UTC) Received: by mail-qk1-f200.google.com with SMTP id s14so673949qkg.12 for ; Thu, 24 Oct 2019 18:23:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=NwbQTkijrN6NABRO3e2oglmsIqJHoiL95bPmzxB+rNU=; b=VIohoB852zkOjRx1ch5vXZBDM9qRHygjn4jmkOjPIRZeDSqN4zgFUDKBMNYYETGQf7 jBO6fGCbMBRWO/Fp5L1MFUICC2o7OcMeWbYci4js58Wxmc2TjbQtClCTHvSU4E5yAs2u ucUI1hennor5TnPO3k2VfeWcITLARrAoj2cqwjfHaaJ51epFazaq0IjJX106h+co451a TbyTrHg2ScFF0tPBnAh5aAhjkE5MXA6B5anQtGj7CWf7hNPGSBp20Dm+vrcvcSYwnPHn vDUZLbSvlubZXPzmg5XK5e+UoWgdlb1XHKRpDEeaY3Hr+NGgT7VAYU2ztO2NU+8CFnZQ mPeA== X-Gm-Message-State: APjAAAXk/JVYk75Gl86UmfuhJ4sXrRBgDWe44/D9mZZXur6S62R1h699 WFUcn+a9VvKMadwbGv6VqBoVzTw5JBob3qAGUWxFYjg0BWyR6vo2XshO2DDC4Ib3HlERn8/nF7f E/2Bm/rf4zXHU+8PR9A4Sd7eroIIRIKVwF7b4bw== X-Received: by 2002:ac8:3209:: with SMTP id x9mr109230qta.293.1571966625635; Thu, 24 Oct 2019 18:23:45 -0700 (PDT) X-Google-Smtp-Source: APXvYqyO6v94I7IikPLSrwDMuhHTpbv4NEcBLDXf5rTMYpQEhtP/Xwd19GgeQoLukJU7OiOS+Ej0c9RMCi+QLzfgiQM= X-Received: by 2002:ac8:3209:: with SMTP id x9mr109211qta.293.1571966625295; Thu, 24 Oct 2019 18:23:45 -0700 (PDT) MIME-Version: 1.0 References: <20191024235120.8059-1-lsahlber@redhat.com> <20191024235120.8059-2-lsahlber@redhat.com> In-Reply-To: <20191024235120.8059-2-lsahlber@redhat.com> From: David Wysochanski Date: Thu, 24 Oct 2019 21:23:09 -0400 Message-ID: Subject: Re: [PATCH] cifs: Fix cifsInodeInfo lock_sem deadlock when reconnect occurs To: Ronnie Sahlberg Cc: linux-cifs Content-Type: text/plain; charset="UTF-8" Sender: linux-cifs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org On Thu, Oct 24, 2019 at 7:51 PM Ronnie Sahlberg wrote: > > From: Dave Wysochanski > > There's a deadlock that is possible and can easily be seen with > a test where multiple readers open/read/close of the same file > and a disruption occurs causing reconnect. The deadlock is due > a reader thread inside cifs_strict_readv calling down_read and > obtaining lock_sem, and then after reconnect inside > cifs_reopen_file calling down_read a second time. If in > between the two down_read calls, a down_write comes from > another process, deadlock occurs. > > CPU0 CPU1 > ---- ---- > cifs_strict_readv() > down_read(&cifsi->lock_sem); > _cifsFileInfo_put > OR > cifs_new_fileinfo > down_write(&cifsi->lock_sem); > cifs_reopen_file() > down_read(&cifsi->lock_sem); > > Fix the above by changing all down_write(lock_sem) calls to > down_write_trylock(lock_sem)/msleep() loop, which in turn > makes the second down_read call benign since it will never > block behind the writer while holding lock_sem. > > Signed-off-by: Dave Wysochanski > Suggested-by: Ronnie Sahlberg > --- > fs/cifs/cifsglob.h | 5 +++++ > fs/cifs/cifsproto.h | 1 + > fs/cifs/file.c | 23 +++++++++++++++-------- > fs/cifs/smb2file.c | 2 +- > 4 files changed, 22 insertions(+), 9 deletions(-) > > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h > index 50dfd9049370..d78bfcc19156 100644 > --- a/fs/cifs/cifsglob.h > +++ b/fs/cifs/cifsglob.h > @@ -1391,6 +1391,11 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file); > struct cifsInodeInfo { > bool can_cache_brlcks; > struct list_head llist; /* locks helb by this inode */ > + /* > + * NOTE: Some code paths call down_read(lock_sem) twice, so > + * we must always use use cifs_down_write() instead of down_write() > + * for this semaphore to avoid deadlocks. > + */ > struct rw_semaphore lock_sem; /* protect the fields above */ > /* BB add in lists for dirty pages i.e. write caching info for oplock */ > struct list_head openFileList; > diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h > index e53e9f62b87b..fe597d3d5208 100644 > --- a/fs/cifs/cifsproto.h > +++ b/fs/cifs/cifsproto.h > @@ -170,6 +170,7 @@ extern int cifs_unlock_range(struct cifsFileInfo *cfile, > struct file_lock *flock, const unsigned int xid); > extern int cifs_push_mandatory_locks(struct cifsFileInfo *cfile); > > +extern void cifs_down_write(struct rw_semaphore *sem); > extern struct cifsFileInfo *cifs_new_fileinfo(struct cifs_fid *fid, > struct file *file, > struct tcon_link *tlink, > diff --git a/fs/cifs/file.c b/fs/cifs/file.c > index 0e0217641de1..a80ec683ea32 100644 > --- a/fs/cifs/file.c > +++ b/fs/cifs/file.c > @@ -281,6 +281,13 @@ cifs_has_mand_locks(struct cifsInodeInfo *cinode) > return has_locks; > } > > +void > +cifs_down_write(struct rw_semaphore *sem) > +{ > + while (!down_write_trylock(sem)) > + msleep(10); > +} > + > struct cifsFileInfo * > cifs_new_fileinfo(struct cifs_fid *fid, struct file *file, > struct tcon_link *tlink, __u32 oplock) > @@ -306,7 +313,7 @@ cifs_new_fileinfo(struct cifs_fid *fid, struct file *file, > INIT_LIST_HEAD(&fdlocks->locks); > fdlocks->cfile = cfile; > cfile->llist = fdlocks; > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > list_add(&fdlocks->llist, &cinode->llist); > up_write(&cinode->lock_sem); > > @@ -464,7 +471,7 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler) > * Delete any outstanding lock records. We'll lose them when the file > * is closed anyway. > */ > - down_write(&cifsi->lock_sem); > + cifs_down_write(&cifsi->lock_sem); > list_for_each_entry_safe(li, tmp, &cifs_file->llist->locks, llist) { > list_del(&li->llist); > cifs_del_lock_waiters(li); > @@ -1027,7 +1034,7 @@ static void > cifs_lock_add(struct cifsFileInfo *cfile, struct cifsLockInfo *lock) > { > struct cifsInodeInfo *cinode = CIFS_I(d_inode(cfile->dentry)); > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > list_add_tail(&lock->llist, &cfile->llist->locks); > up_write(&cinode->lock_sem); > } > @@ -1049,7 +1056,7 @@ cifs_lock_add_if(struct cifsFileInfo *cfile, struct cifsLockInfo *lock, > > try_again: > exist = false; > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > > exist = cifs_find_lock_conflict(cfile, lock->offset, lock->length, > lock->type, lock->flags, &conf_lock, > @@ -1072,7 +1079,7 @@ cifs_lock_add_if(struct cifsFileInfo *cfile, struct cifsLockInfo *lock, > (lock->blist.next == &lock->blist)); > if (!rc) > goto try_again; > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > list_del_init(&lock->blist); > } > > @@ -1125,7 +1132,7 @@ cifs_posix_lock_set(struct file *file, struct file_lock *flock) > return rc; > > try_again: > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > if (!cinode->can_cache_brlcks) { > up_write(&cinode->lock_sem); > return rc; > @@ -1331,7 +1338,7 @@ cifs_push_locks(struct cifsFileInfo *cfile) > int rc = 0; > > /* we are going to update can_cache_brlcks here - need a write access */ > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > if (!cinode->can_cache_brlcks) { > up_write(&cinode->lock_sem); > return rc; > @@ -1522,7 +1529,7 @@ cifs_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock, > if (!buf) > return -ENOMEM; > > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > for (i = 0; i < 2; i++) { > cur = buf; > num = 0; > diff --git a/fs/cifs/smb2file.c b/fs/cifs/smb2file.c > index e6a1fc72018f..8b0b512c5792 100644 > --- a/fs/cifs/smb2file.c > +++ b/fs/cifs/smb2file.c > @@ -145,7 +145,7 @@ smb2_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock, > > cur = buf; > > - down_write(&cinode->lock_sem); > + cifs_down_write(&cinode->lock_sem); > list_for_each_entry_safe(li, tmp, &cfile->llist->locks, llist) { > if (flock->fl_start > li->offset || > (flock->fl_start + length) < > -- > 2.13.6 > Thanks for doing this! Looks fine to me. I'm not loving this approach to solve this problem but I understand why it may be preferred right now. I note that trylock with a sleep / retry loop is not often used in filesystems that I could tell (though it is used in drivers), so maybe this can be improved another day.