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([43.135.149.86]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22ac7c95cdcsm53279515ad.118.2025.04.11.11.31.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Apr 2025 11:31:27 -0700 (PDT) From: alexjlzheng@gmail.com X-Google-Original-From: alexjlzheng@tencent.com To: gregkh@linuxfoundation.org, tj@kernel.org Cc: alexjlzheng@tencent.com, linux-kernel@vger.kernel.org Subject: [PATCH kernfs 3/3] kernfs: switch global kernfs_pr_cont_lock to per-fs lock Date: Sat, 12 Apr 2025 02:31:09 +0800 Message-ID: <20250411183109.6334-4-alexjlzheng@tencent.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250411183109.6334-1-alexjlzheng@tencent.com> References: <20250411183109.6334-1-alexjlzheng@tencent.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Jinliang Zheng The kernfs implementation has big lock granularity(kernfs_pr_cont_lock) so every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the lock. This patch switches the global kernfs_pr_cont_lock to per-fs lock, which put the spinlock into kernfs_root. Of course, kernfs_pr_cont_buf also needs to be moved to kernfs_root. Signed-off-by: Jinliang Zheng --- fs/kernfs/dir.c | 46 +++++++++++++++++-------------------- fs/kernfs/kernfs-internal.h | 11 +++++++++ 2 files changed, 32 insertions(+), 25 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index d63a96786c9b..29605d7f0ab0 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -17,16 +17,6 @@ =20 #include "kernfs-internal.h" =20 -/* - * Don't use rename_lock to piggy back on pr_cont_buf. We don't want to - * call pr_cont() while holding rename_lock. Because sometimes pr_cont() - * will perform wakeups when releasing console_sem. Holding rename_lock - * will introduce deadlock if the scheduler reads the kernfs_name in the - * wakeup path. - */ -static DEFINE_SPINLOCK(kernfs_pr_cont_lock); -static char kernfs_pr_cont_buf[PATH_MAX]; /* protected by pr_cont_lock */ - #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb) =20 static bool __kernfs_active(struct kernfs_node *kn) @@ -244,13 +234,15 @@ EXPORT_SYMBOL_GPL(kernfs_path_from_node); void pr_cont_kernfs_name(struct kernfs_node *kn) { unsigned long flags; + struct kernfs_root *root =3D kernfs_root(kn); =20 - spin_lock_irqsave(&kernfs_pr_cont_lock, flags); + spin_lock_irqsave(&root->kernfs_pr_cont_lock, flags); =20 - kernfs_name(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf)); - pr_cont("%s", kernfs_pr_cont_buf); + kernfs_name(kn, root->kernfs_pr_cont_buf, + sizeof(root->kernfs_pr_cont_buf)); + pr_cont("%s", root->kernfs_pr_cont_buf); =20 - spin_unlock_irqrestore(&kernfs_pr_cont_lock, flags); + spin_unlock_irqrestore(&root->kernfs_pr_cont_lock, flags); } =20 /** @@ -263,11 +255,12 @@ void pr_cont_kernfs_path(struct kernfs_node *kn) { unsigned long flags; int sz; + struct kernfs_root *root =3D kernfs_root(kn); =20 - spin_lock_irqsave(&kernfs_pr_cont_lock, flags); + spin_lock_irqsave(&root->kernfs_pr_cont_lock, flags); =20 - sz =3D kernfs_path_from_node(kn, NULL, kernfs_pr_cont_buf, - sizeof(kernfs_pr_cont_buf)); + sz =3D kernfs_path_from_node(kn, NULL, root->kernfs_pr_cont_buf, + sizeof(root->kernfs_pr_cont_buf)); if (sz < 0) { if (sz =3D=3D -E2BIG) pr_cont("(name too long)"); @@ -276,10 +269,10 @@ void pr_cont_kernfs_path(struct kernfs_node *kn) goto out; } =20 - pr_cont("%s", kernfs_pr_cont_buf); + pr_cont("%s", root->kernfs_pr_cont_buf); =20 out: - spin_unlock_irqrestore(&kernfs_pr_cont_lock, flags); + spin_unlock_irqrestore(&root->kernfs_pr_cont_lock, flags); } =20 /** @@ -888,19 +881,21 @@ static struct kernfs_node *kernfs_walk_ns(struct kern= fs_node *parent, { ssize_t len; char *p, *name; + struct kernfs_root *root =3D kernfs_root(parent); =20 - lockdep_assert_held_read(&kernfs_root(parent)->kernfs_rwsem); + lockdep_assert_held_read(&root->kernfs_rwsem); =20 - spin_lock_irq(&kernfs_pr_cont_lock); + spin_lock_irq(&root->kernfs_pr_cont_lock); =20 - len =3D strscpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf)); + len =3D strscpy(root->kernfs_pr_cont_buf, path, + sizeof(root->kernfs_pr_cont_buf)); =20 if (len < 0) { - spin_unlock_irq(&kernfs_pr_cont_lock); + spin_unlock_irq(&root->kernfs_pr_cont_lock); return NULL; } =20 - p =3D kernfs_pr_cont_buf; + p =3D root->kernfs_pr_cont_buf; =20 while ((name =3D strsep(&p, "/")) && parent) { if (*name =3D=3D '\0') @@ -908,7 +903,7 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs= _node *parent, parent =3D kernfs_find_ns(parent, name, ns); } =20 - spin_unlock_irq(&kernfs_pr_cont_lock); + spin_unlock_irq(&root->kernfs_pr_cont_lock); =20 return parent; } @@ -995,6 +990,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_sy= scall_ops *scops, init_rwsem(&root->kernfs_supers_rwsem); INIT_LIST_HEAD(&root->supers); rwlock_init(&root->kernfs_rename_lock); + spin_lock_init(&root->kernfs_pr_cont_lock); =20 /* * On 64bit ino setups, id is ino. On 32bit, low 32bits are ino. diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h index 6061b6f70d2a..c7fe50955e8c 100644 --- a/fs/kernfs/kernfs-internal.h +++ b/fs/kernfs/kernfs-internal.h @@ -55,6 +55,17 @@ struct kernfs_root { rwlock_t kernfs_rename_lock; =20 struct rcu_head rcu; + + /* + * Don't use rename_lock to piggy back on pr_cont_buf. We don't want to + * call pr_cont() while holding rename_lock. Because sometimes pr_cont() + * will perform wakeups when releasing console_sem. Holding rename_lock + * will introduce deadlock if the scheduler reads the kernfs_name in the + * wakeup path. + */ + spinlock_t kernfs_pr_cont_lock; + /* protected by pr_cont_lock */ + char kernfs_pr_cont_buf[PATH_MAX]; }; =20 /* +1 to avoid triggering overflow warning when negating it */ --=20 2.48.1