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(cola.collaboradmins.com [195.201.22.229]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: ehristev) by madrid.collaboradmins.com (Postfix) with ESMTPSA id 5605737821F2; Fri, 5 Jul 2024 06:26:52 +0000 (UTC) From: Eugen Hristev To: viro@zeniv.linux.org.uk, brauner@kernel.org, tytso@mit.edu, linux-ext4@vger.kernel.org Cc: jack@suse.cz, adilger.kernel@dilger.ca, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, krisman@suse.de, kernel@collabora.com, shreeya.patel@collabora.com, Eugen Hristev Subject: [PATCH 1/2] fs/dcache: introduce d_alloc_parallel_check_existing Date: Fri, 5 Jul 2024 09:26:20 +0300 Message-Id: <20240705062621.630604-2-eugen.hristev@collabora.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240705062621.630604-1-eugen.hristev@collabora.com> References: <20240705062621.630604-1-eugen.hristev@collabora.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 d_alloc_parallel currently looks for entries that match the name being added and return them if found. However if d_alloc_parallel is being called during the process of adding a new entry (that becomes in_lookup), the same entry is found by d_alloc_parallel in the in_lookup_hash and d_alloc_parallel will wait forever for it to stop being in lookup. To avoid this, it makes sense to check for an entry being currently added (e.g. by d_add_ci from a lookup func, like xfs is doing) and if this exact match is found, return the entry. This way, to add a new entry , as xfs is doing, is the following flow: _lookup_slow -> d_alloc_parallel -> entry is being created -> xfs_lookup -> d_add_ci -> d_alloc_parallel_check_existing(entry created before) -> d_splice_alias. The initial entry stops being in_lookup after d_splice_alias finishes, and it's returned to d_add_ci by d_alloc_parallel_check_existing. Without d_alloc_parallel_check_existing, d_alloc_parallel would be called instead and wait forever for the entry to stop being in lookup, as the iteration through the in_lookup_hash matches the entry. Currently XFS does not hang because it creates another entry in the second call of d_alloc_parallel if the name differs by case as the hashing and comparison functions used by XFS are not case insensitive. Signed-off-by: Eugen Hristev --- fs/dcache.c | 29 +++++++++++++++++++++++------ include/linux/dcache.h | 4 ++++ 2 files changed, 27 insertions(+), 6 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index a0a944fd3a1c..459a3d8b8bdb 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2049,8 +2049,9 @@ struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode, return found; } if (d_in_lookup(dentry)) { - found = d_alloc_parallel(dentry->d_parent, name, - dentry->d_wait); + found = d_alloc_parallel_check_existing(dentry, + dentry->d_parent, name, + dentry->d_wait); if (IS_ERR(found) || !d_in_lookup(found)) { iput(inode); return found; @@ -2452,9 +2453,10 @@ static void d_wait_lookup(struct dentry *dentry) } } -struct dentry *d_alloc_parallel(struct dentry *parent, - const struct qstr *name, - wait_queue_head_t *wq) +struct dentry *d_alloc_parallel_check_existing(struct dentry *d_check, + struct dentry *parent, + const struct qstr *name, + wait_queue_head_t *wq) { unsigned int hash = name->hash; struct hlist_bl_head *b = in_lookup_hash(parent, hash); @@ -2523,6 +2525,14 @@ struct dentry *d_alloc_parallel(struct dentry *parent, } rcu_read_unlock(); + + /* if the entry we found is the same as the original we + * are checking against, then return it + */ + if (d_check == dentry) { + dput(new); + return dentry; + } /* * somebody is likely to be still doing lookup for it; * wait for them to finish @@ -2560,8 +2570,15 @@ struct dentry *d_alloc_parallel(struct dentry *parent, dput(dentry); goto retry; } -EXPORT_SYMBOL(d_alloc_parallel); +EXPORT_SYMBOL(d_alloc_parallel_check_existing); +struct dentry *d_alloc_parallel(struct dentry *parent, + const struct qstr *name, + wait_queue_head_t *wq) +{ + return d_alloc_parallel_check_existing(NULL, parent, name, wq); +} +EXPORT_SYMBOL(d_alloc_parallel); /* * - Unhash the dentry * - Retrieve and clear the waitqueue head in dentry diff --git a/include/linux/dcache.h b/include/linux/dcache.h index bf53e3894aae..6eb21a518cb0 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -232,6 +232,10 @@ extern struct dentry * d_alloc(struct dentry *, const struct qstr *); extern struct dentry * d_alloc_anon(struct super_block *); extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *, wait_queue_head_t *); +extern struct dentry * d_alloc_parallel_check_existing(struct dentry *, + struct dentry *, + const struct qstr *, + wait_queue_head_t *); extern struct dentry * d_splice_alias(struct inode *, struct dentry *); extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *); extern bool d_same_name(const struct dentry *dentry, const struct dentry *parent, From patchwork Fri Jul 5 06:26:21 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eugen Hristev X-Patchwork-Id: 1957125 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@legolas.ozlabs.org Authentication-Results: legolas.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=collabora.com header.i=@collabora.com header.a=rsa-sha256 header.s=mail header.b=tROV6jtp; 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(cola.collaboradmins.com [195.201.22.229]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: ehristev) by madrid.collaboradmins.com (Postfix) with ESMTPSA id 4E25837821F8; Fri, 5 Jul 2024 06:26:53 +0000 (UTC) From: Eugen Hristev To: viro@zeniv.linux.org.uk, brauner@kernel.org, tytso@mit.edu, linux-ext4@vger.kernel.org Cc: jack@suse.cz, adilger.kernel@dilger.ca, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, krisman@suse.de, kernel@collabora.com, shreeya.patel@collabora.com, Eugen Hristev Subject: [PATCH 2/2] ext4: in lookup call d_add_ci if there is a case mismatch Date: Fri, 5 Jul 2024 09:26:21 +0300 Message-Id: <20240705062621.630604-3-eugen.hristev@collabora.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240705062621.630604-1-eugen.hristev@collabora.com> References: <20240705062621.630604-1-eugen.hristev@collabora.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In lookup function, if we have a file match but not a case match in the case-insensitive case, call d_add_ci to store the real filename into cache instead of the case variant of the name that was looked up. This avoids exposing into user space (e.g. /proc/self/cwd) internal cache data. Signed-off-by: Eugen Hristev --- fs/ext4/namei.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index e6769b97a970..0676c21e1622 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1834,6 +1834,19 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, unsi return NULL; } + /* Create a case-insensitive cache entry with the real + * name stored, in case our search pattern differs + * in terms of case. + */ + if (inode && IS_CASEFOLDED(dir) && + memcmp(de->name, dentry->d_name.name, de->name_len)) { + struct qstr dname; + + dname.len = de->name_len; + dname.name = de->name; + return d_add_ci(dentry, inode, &dname); + } + return d_splice_alias(inode, dentry); }