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Message-ID: <ZOkj9uTkoHPR/tDV@dread.disaster.area> Date: Sat, 26 Aug 2023 07:58:14 +1000 From: Dave Chinner <david@...morbit.com> To: Hao Xu <hao.xu@...ux.dev> Cc: io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>, Dominique Martinet <asmadeus@...ewreck.org>, Pavel Begunkov <asml.silence@...il.com>, Christian Brauner <brauner@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>, "Darrick J . Wong" <djwong@...nel.org>, linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, linux-cachefs@...hat.com, ecryptfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-unionfs@...r.kernel.org, bpf@...r.kernel.org, netdev@...r.kernel.org, linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org, codalist@...a.cs.cmu.edu, linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com, linux-mm@...ck.org, linux-nilfs@...r.kernel.org, devel@...ts.orangefs.org, linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org, linux-mtd@...ts.infradead.org, Wanpeng Li <wanpengli@...cent.com> Subject: Re: [PATCH 26/29] xfs: return -EAGAIN when nowait meets sync in transaction commit On Fri, Aug 25, 2023 at 09:54:28PM +0800, Hao Xu wrote: > From: Hao Xu <howeyxu@...cent.com> > > if the log transaction is a sync one, let's fail the nowait try and > return -EAGAIN directly since sync transaction means blocked by IO. > > Signed-off-by: Hao Xu <howeyxu@...cent.com> > --- > fs/xfs/xfs_trans.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > index 7988b4c7f36e..f1f84a3dd456 100644 > --- a/fs/xfs/xfs_trans.c > +++ b/fs/xfs/xfs_trans.c > @@ -968,12 +968,24 @@ __xfs_trans_commit( > xfs_csn_t commit_seq = 0; > int error = 0; > int sync = tp->t_flags & XFS_TRANS_SYNC; > + bool nowait = tp->t_flags & XFS_TRANS_NOWAIT; > + bool perm_log = tp->t_flags & XFS_TRANS_PERM_LOG_RES; > > trace_xfs_trans_commit(tp, _RET_IP_); > > + if (nowait && sync) { > + /* > + * Currently nowait is only from xfs_vn_update_time() > + * so perm_log is always false here, but let's make > + * code general. > + */ > + if (perm_log) > + xfs_defer_cancel(tp); > + goto out_unreserve; > + } This is fundamentally broken. We cannot about a transaction commit with dirty items at this point with shutting down the filesystem. This points to XFS_TRANS_NOWAIT being completely broken, too, because we don't call xfs_trans_set_sync() until just before we commit the transaction. At this point, it is -too late- for nowait+sync to be handled gracefully, and it will *always* go bad. IOWs, the whole transaction "nowait" semantics as designed and implemented is not a workable solution.... -Dave. -- Dave Chinner david@...morbit.com
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