From: NeilBrown <neilb@suse.com> To: Andreas Gruenbacher <agruenba@redhat.com>, cluster-devel@redhat.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Graf <tgraf@suug.ch>, Herbert Xu <herbert@gondor.apana.org.au>, Tom Herbert <tom@quantonium.net> Subject: Re: [PATCH] gfs2: Stop using rhashtable_walk_peek Date: Thu, 29 Mar 2018 08:53:19 +1100 [thread overview] Message-ID: <87woxv3m0g.fsf@notabene.neil.brown.name> (raw) In-Reply-To: <20180328160009.29633-1-agruenba@redhat.com> [-- Attachment #1: Type: text/plain, Size: 2913 bytes --] On Wed, Mar 28 2018, Andreas Gruenbacher wrote: > Function rhashtable_walk_peek is problematic because there is no > guarantee that the glock previously returned still exists; when that key > is deleted, rhashtable_walk_peek can end up returning a different key, > which would cause an inconsistent glock dump. So instead of using > rhashtable_walk_peek, keep track of the current glock in the seq file > iterator functions. > > Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> > --- > fs/gfs2/glock.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > > diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c > index 82fb5583445c..f1fc353875d3 100644 > --- a/fs/gfs2/glock.c > +++ b/fs/gfs2/glock.c > @@ -55,6 +55,7 @@ struct gfs2_glock_iter { > struct gfs2_sbd *sdp; /* incore superblock */ > struct rhashtable_iter hti; /* rhashtable iterator */ > struct gfs2_glock *gl; /* current glock struct */ > + bool gl_held; > loff_t last_pos; /* last position */ > }; > > @@ -1923,9 +1924,11 @@ void gfs2_glock_exit(void) > > static void gfs2_glock_iter_next(struct gfs2_glock_iter *gi, loff_t n) > { > - if (n == 0) > - gi->gl = rhashtable_walk_peek(&gi->hti); > - else { > + if (n != 0 || !gi->gl) { > + if (gi->gl_held) { > + gfs2_glock_queue_put(gi->gl); > + gi->gl_held = false; > + } > gi->gl = rhashtable_walk_next(&gi->hti); > n--; > } Thank for this patch! The above looks a bit fragile to me. gfs2_glock_iter_next() (And hence gfs2_glock_seq_start()) will sometimes exit with gl_held true, and sometimes with it false. gfs2_glock_seq_stop() assumes that it is false. Normally gfs2_glock_seq_next() will normally be called between these two and will clear gl_held, but I don't think there is a hard guarantee of that. Maybe we should always 'put' gi->gl in iter_next if gl_held?? Thanks, NeilBrown > @@ -1988,7 +1991,10 @@ static void gfs2_glock_seq_stop(struct seq_file *seq, void *iter_ptr) > { > struct gfs2_glock_iter *gi = seq->private; > > - gi->gl = NULL; > + if (gi->gl) { > + lockref_get(&gi->gl->gl_lockref); > + gi->gl_held = true; > + } > rhashtable_walk_stop(&gi->hti); > } > > @@ -2061,6 +2067,7 @@ static int __gfs2_glocks_open(struct inode *inode, struct file *file, > */ > gi->last_pos = -1; > gi->gl = NULL; > + gi->gl_held = false; > rhashtable_walk_enter(&gl_hash_table, &gi->hti); > } > return ret; > @@ -2076,7 +2083,8 @@ static int gfs2_glocks_release(struct inode *inode, struct file *file) > struct seq_file *seq = file->private_data; > struct gfs2_glock_iter *gi = seq->private; > > - gi->gl = NULL; > + if (gi->gl_held) > + gfs2_glock_put(gi->gl); > rhashtable_walk_exit(&gi->hti); > return seq_release_private(inode, file); > } > -- > 2.14.3 [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 832 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: NeilBrown <neilb@suse.com> To: cluster-devel.redhat.com Subject: [Cluster-devel] [PATCH] gfs2: Stop using rhashtable_walk_peek Date: Thu, 29 Mar 2018 08:53:19 +1100 [thread overview] Message-ID: <87woxv3m0g.fsf@notabene.neil.brown.name> (raw) In-Reply-To: <20180328160009.29633-1-agruenba@redhat.com> On Wed, Mar 28 2018, Andreas Gruenbacher wrote: > Function rhashtable_walk_peek is problematic because there is no > guarantee that the glock previously returned still exists; when that key > is deleted, rhashtable_walk_peek can end up returning a different key, > which would cause an inconsistent glock dump. So instead of using > rhashtable_walk_peek, keep track of the current glock in the seq file > iterator functions. > > Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> > --- > fs/gfs2/glock.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > > diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c > index 82fb5583445c..f1fc353875d3 100644 > --- a/fs/gfs2/glock.c > +++ b/fs/gfs2/glock.c > @@ -55,6 +55,7 @@ struct gfs2_glock_iter { > struct gfs2_sbd *sdp; /* incore superblock */ > struct rhashtable_iter hti; /* rhashtable iterator */ > struct gfs2_glock *gl; /* current glock struct */ > + bool gl_held; > loff_t last_pos; /* last position */ > }; > > @@ -1923,9 +1924,11 @@ void gfs2_glock_exit(void) > > static void gfs2_glock_iter_next(struct gfs2_glock_iter *gi, loff_t n) > { > - if (n == 0) > - gi->gl = rhashtable_walk_peek(&gi->hti); > - else { > + if (n != 0 || !gi->gl) { > + if (gi->gl_held) { > + gfs2_glock_queue_put(gi->gl); > + gi->gl_held = false; > + } > gi->gl = rhashtable_walk_next(&gi->hti); > n--; > } Thank for this patch! The above looks a bit fragile to me. gfs2_glock_iter_next() (And hence gfs2_glock_seq_start()) will sometimes exit with gl_held true, and sometimes with it false. gfs2_glock_seq_stop() assumes that it is false. Normally gfs2_glock_seq_next() will normally be called between these two and will clear gl_held, but I don't think there is a hard guarantee of that. Maybe we should always 'put' gi->gl in iter_next if gl_held?? Thanks, NeilBrown > @@ -1988,7 +1991,10 @@ static void gfs2_glock_seq_stop(struct seq_file *seq, void *iter_ptr) > { > struct gfs2_glock_iter *gi = seq->private; > > - gi->gl = NULL; > + if (gi->gl) { > + lockref_get(&gi->gl->gl_lockref); > + gi->gl_held = true; > + } > rhashtable_walk_stop(&gi->hti); > } > > @@ -2061,6 +2067,7 @@ static int __gfs2_glocks_open(struct inode *inode, struct file *file, > */ > gi->last_pos = -1; > gi->gl = NULL; > + gi->gl_held = false; > rhashtable_walk_enter(&gl_hash_table, &gi->hti); > } > return ret; > @@ -2076,7 +2083,8 @@ static int gfs2_glocks_release(struct inode *inode, struct file *file) > struct seq_file *seq = file->private_data; > struct gfs2_glock_iter *gi = seq->private; > > - gi->gl = NULL; > + if (gi->gl_held) > + gfs2_glock_put(gi->gl); > rhashtable_walk_exit(&gi->hti); > return seq_release_private(inode, file); > } > -- > 2.14.3 -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 832 bytes Desc: not available URL: <http://listman.redhat.com/archives/cluster-devel/attachments/20180329/cd2b1142/attachment.sig>
next prev parent reply other threads:[~2018-03-28 21:53 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-03-28 16:00 [PATCH] gfs2: Stop using rhashtable_walk_peek Andreas Gruenbacher 2018-03-28 16:00 ` [Cluster-devel] " Andreas Gruenbacher 2018-03-28 21:53 ` NeilBrown [this message] 2018-03-28 21:53 ` NeilBrown 2018-03-28 22:58 ` Andreas Gruenbacher 2018-03-28 22:58 ` [Cluster-devel] " Andreas Gruenbacher
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