vfs: Use sequence counter with associated spinlock

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-19-a.darwish@linutronix.de

diff --git a/fs/dcache.c b/fs/dcache.c
index 361ea7ab30ea7d95ef00b9b3060e61d4275501c9..ea0485861d9377311a858359ab1183a1bae4e042 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1746,7 +1746,7 @@ static struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
        dentry->d_lockref.count = 1;
        dentry->d_flags = 0;
        spin_lock_init(&dentry->d_lock);
-       seqcount_init(&dentry->d_seq);
+       seqcount_spinlock_init(&dentry->d_seq, &dentry->d_lock);
        dentry->d_inode = NULL;
        dentry->d_parent = dentry;
        dentry->d_sb = sb;

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index ca639ed967b7a66c489b2e14e675df2e0cbca247..04b3f5b9c6295e196e16af5cc0eda6ada62a7c7c 100644 (file)
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -117,7 +117,7 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
                fs->users = 1;
                fs->in_exec = 0;
                spin_lock_init(&fs->lock);
-               seqcount_init(&fs->seq);
+               seqcount_spinlock_init(&fs->seq, &fs->lock);
                fs->umask = old->umask;
 
                spin_lock(&old->lock);
@@ -163,6 +163,6 @@ EXPORT_SYMBOL(current_umask);
 struct fs_struct init_fs = {
        .users          = 1,
        .lock           = __SPIN_LOCK_UNLOCKED(init_fs.lock),
-       .seq            = SEQCNT_ZERO(init_fs.seq),
+       .seq            = SEQCNT_SPINLOCK_ZERO(init_fs.seq, &init_fs.lock),
        .umask          = 0022,
 };

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index a81f0c3cf352994fcc6c00c3422a8ee12f1979d8..65d975bf9390427f7cef96dd323642a6b00250d2 100644 (file)
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -89,7 +89,7 @@ extern struct dentry_stat_t dentry_stat;
 struct dentry {
        /* RCU lookup touched fields */
        unsigned int d_flags;           /* protected by d_lock */
-       seqcount_t d_seq;               /* per dentry seqlock */
+       seqcount_spinlock_t d_seq;      /* per dentry seqlock */
        struct hlist_bl_node d_hash;    /* lookup hash list */
        struct dentry *d_parent;        /* parent directory */
        struct qstr d_name;

diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h
index cf1015abfbf238082c89ae99650bea83c3fb290f..783b48dedb723f159a822cd8debcd533d713457f 100644 (file)
--- a/include/linux/fs_struct.h
+++ b/include/linux/fs_struct.h
@@ -9,7 +9,7 @@
 struct fs_struct {
        int users;
        spinlock_t lock;
-       seqcount_t seq;
+       seqcount_spinlock_t seq;
        int umask;
        int in_exec;
        struct path root, pwd;