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Thu, 12 Mar 2026 20:46:58 -0400 (EDT) From: NeilBrown To: Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , Jeff Layton , Trond Myklebust , Anna Schumaker , Carlos Maiolino , Miklos Szeredi , Amir Goldstein , Jan Harkes , Hugh Dickins , Baolin Wang , David Howells , Marc Dionne , Steve French , Namjae Jeon , Sungjong Seo , Yuezhang Mo , Andreas Hindborg , Breno Leitao , "Theodore Ts'o" , Andreas Dilger , Steven Rostedt , Masami Hiramatsu , Ilya Dryomov , Alex Markuze , Viacheslav Dubeyko , Tyler Hicks , Andreas Gruenbacher , Richard Weinberger , Anton Ivanov , Johannes Berg , Jeremy Kerr , Ard Biesheuvel Cc: linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-unionfs@vger.kernel.org, coda@cs.cmu.edu, linux-mm@kvack.org, linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, ceph-devel@vger.kernel.org, ecryptfs@vger.kernel.org, gfs2@lists.linux.dev, linux-um@lists.infradead.org, linux-efi@vger.kernel.org Subject: [PATCH 23/53] afs: lookup_atsys to drop and reclaim lock. Date: Fri, 13 Mar 2026 08:12:10 +1100 Message-ID: <20260312214330.3885211-24-neilb@ownmail.net> X-Mailer: git-send-email 2.50.0.107.gf914562f5916.dirty In-Reply-To: <20260312214330.3885211-1-neilb@ownmail.net> References: <20260312214330.3885211-1-neilb@ownmail.net> Reply-To: NeilBrown MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AEF4A180006 X-Stat-Signature: oc7xx881j4cmwask74a9874rmksiajtm X-Rspam-User: X-HE-Tag: 1773362834-961420 X-HE-Meta: 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 022h7mKa 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: NeilBrown If afs is asked to lookup a name ending with @sys, it needs to look up a different name for which is allocates a dentry with d_alloc_parallel(). This is done while the parent lock is held which will be a problem in a future patch where the ordering of the parent lock and d_alloc_parallel() locking is reversed. There is no actual need to hold the lock while d_alloc_parallel() is called, so with this patch we drop the lock and reclaim it. Signed-off-by: NeilBrown --- fs/afs/dir.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/fs/afs/dir.c b/fs/afs/dir.c index 1e472768e1f1..c195ee851191 100644 --- a/fs/afs/dir.c +++ b/fs/afs/dir.c @@ -908,12 +908,14 @@ static struct inode *afs_do_lookup(struct inode *dir, struct dentry *dentry) /* * Look up an entry in a directory with @sys substitution. */ -static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry) +static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry, + unsigned int flags) { struct afs_sysnames *subs; struct afs_net *net = afs_i2net(dir); struct dentry *ret; char *buf, *p, *name; + struct qstr nm; int len, i; _enter(""); @@ -933,6 +935,13 @@ static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry) refcount_inc(&subs->usage); read_unlock(&net->sysnames_lock); + /* Calling d_alloc_parallel() while holding parent locked is undesirable. + * We don't really need the lock any more. + */ + if (flags & LOOKUP_SHARED) + inode_unlock_shared(dir); + else + inode_unlock(dir); for (i = 0; i < subs->nr; i++) { name = subs->subs[i]; len = dentry->d_name.len - 4 + strlen(name); @@ -942,7 +951,10 @@ static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry) } strcpy(p, name); - ret = lookup_noperm(&QSTR(buf), dentry->d_parent); + nm = QSTR(buf); + ret = try_lookup_noperm(&nm, dentry->d_parent); + if (!ret) + ret = d_alloc_parallel(dentry->d_parent, &nm); if (IS_ERR(ret) || d_is_positive(ret)) goto out_s; dput(ret); @@ -953,6 +965,10 @@ static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry) */ ret = NULL; out_s: + if (flags & LOOKUP_SHARED) + inode_lock_shared(dir); + else + inode_lock_nested(dir, I_MUTEX_PARENT); afs_put_sysnames(subs); kfree(buf); out_p: @@ -998,7 +1014,7 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry, dentry->d_name.name[dentry->d_name.len - 3] == 's' && dentry->d_name.name[dentry->d_name.len - 2] == 'y' && dentry->d_name.name[dentry->d_name.len - 1] == 's') - return afs_lookup_atsys(dir, dentry); + return afs_lookup_atsys(dir, dentry, flags); afs_stat_v(dvnode, n_lookup); inode = afs_do_lookup(dir, dentry); -- 2.50.0.107.gf914562f5916.dirty