]> git.karo-electronics.de Git - karo-tx-linux.git/blobdiff - fs/dcache.c
Merge remote-tracking branch 'fuse/for-next'
[karo-tx-linux.git] / fs / dcache.c
index 4d9df3c940e697603ca41aec60f7fc97c3361ada..d70df2e0e0da8a6b41d9bfeba798fb4cc9481a80 100644 (file)
@@ -37,6 +37,7 @@
 #include <linux/rculist_bl.h>
 #include <linux/prefetch.h>
 #include <linux/ratelimit.h>
+#include <linux/list_lru.h>
 #include "internal.h"
 #include "mount.h"
 
@@ -48,7 +49,7 @@
  *   - the dcache hash table
  * s_anon bl list spinlock protects:
  *   - the s_anon list (see __d_drop)
- * dcache_lru_lock protects:
+ * dentry->d_sb->s_dentry_lru_lock protects:
  *   - the dcache lru lists and counters
  * d_lock protects:
  *   - d_flags
@@ -63,7 +64,7 @@
  * Ordering:
  * dentry->d_inode->i_lock
  *   dentry->d_lock
- *     dcache_lru_lock
+ *     dentry->d_sb->s_dentry_lru_lock
  *     dcache_hash_bucket lock
  *     s_anon lock
  *
@@ -81,7 +82,6 @@
 int sysctl_vfs_cache_pressure __read_mostly = 100;
 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 
-static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 
 EXPORT_SYMBOL(rename_lock);
@@ -90,8 +90,8 @@ static struct kmem_cache *dentry_cache __read_mostly;
 
 /**
  * read_seqbegin_or_lock - begin a sequence number check or locking block
- * lock: sequence lock
- * seq : sequence number to be checked
+ * @lock: sequence lock
+ * @seq : sequence number to be checked
  *
  * First try it once optimistically without taking the lock. If that fails,
  * take the lock. The sequence number is also used as a marker for deciding
@@ -103,7 +103,7 @@ static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
        if (!(*seq & 1))        /* Even */
                *seq = read_seqbegin(lock);
        else                    /* Odd */
-               write_seqlock(lock);
+               read_seqlock_excl(lock);
 }
 
 static inline int need_seqretry(seqlock_t *lock, int seq)
@@ -114,7 +114,7 @@ static inline int need_seqretry(seqlock_t *lock, int seq)
 static inline void done_seqretry(seqlock_t *lock, int seq)
 {
        if (seq & 1)
-               write_sequnlock(lock);
+               read_sequnlock_excl(lock);
 }
 
 /*
@@ -146,23 +146,47 @@ struct dentry_stat_t dentry_stat = {
        .age_limit = 45,
 };
 
-static DEFINE_PER_CPU(unsigned int, nr_dentry);
+static DEFINE_PER_CPU(long, nr_dentry);
+static DEFINE_PER_CPU(long, nr_dentry_unused);
 
 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
-static int get_nr_dentry(void)
+
+/*
+ * Here we resort to our own counters instead of using generic per-cpu counters
+ * for consistency with what the vfs inode code does. We are expected to harvest
+ * better code and performance by having our own specialized counters.
+ *
+ * Please note that the loop is done over all possible CPUs, not over all online
+ * CPUs. The reason for this is that we don't want to play games with CPUs going
+ * on and off. If one of them goes off, we will just keep their counters.
+ *
+ * glommer: See cffbc8a for details, and if you ever intend to change this,
+ * please update all vfs counters to match.
+ */
+static long get_nr_dentry(void)
 {
        int i;
-       int sum = 0;
+       long sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_dentry, i);
        return sum < 0 ? 0 : sum;
 }
 
+static long get_nr_dentry_unused(void)
+{
+       int i;
+       long sum = 0;
+       for_each_possible_cpu(i)
+               sum += per_cpu(nr_dentry_unused, i);
+       return sum < 0 ? 0 : sum;
+}
+
 int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
                   size_t *lenp, loff_t *ppos)
 {
        dentry_stat.nr_dentry = get_nr_dentry();
-       return proc_dointvec(table, write, buffer, lenp, ppos);
+       dentry_stat.nr_unused = get_nr_dentry_unused();
+       return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 }
 #endif
 
@@ -333,52 +357,96 @@ static void dentry_unlink_inode(struct dentry * dentry)
 }
 
 /*
- * dentry_lru_(add|del|prune|move_tail) must be called with d_lock held.
+ * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
+ * is in use - which includes both the "real" per-superblock
+ * LRU list _and_ the DCACHE_SHRINK_LIST use.
+ *
+ * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
+ * on the shrink list (ie not on the superblock LRU list).
+ *
+ * The per-cpu "nr_dentry_unused" counters are updated with
+ * the DCACHE_LRU_LIST bit.
+ *
+ * These helper functions make sure we always follow the
+ * rules. d_lock must be held by the caller.
  */
-static void dentry_lru_add(struct dentry *dentry)
+#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
+static void d_lru_add(struct dentry *dentry)
 {
-       if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST))) {
-               spin_lock(&dcache_lru_lock);
-               dentry->d_flags |= DCACHE_LRU_LIST;
-               list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
-               dentry->d_sb->s_nr_dentry_unused++;
-               dentry_stat.nr_unused++;
-               spin_unlock(&dcache_lru_lock);
-       }
+       D_FLAG_VERIFY(dentry, 0);
+       dentry->d_flags |= DCACHE_LRU_LIST;
+       this_cpu_inc(nr_dentry_unused);
+       WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
 }
 
-static void __dentry_lru_del(struct dentry *dentry)
+static void d_lru_del(struct dentry *dentry)
 {
+       D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+       dentry->d_flags &= ~DCACHE_LRU_LIST;
+       this_cpu_dec(nr_dentry_unused);
+       WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+}
+
+static void d_shrink_del(struct dentry *dentry)
+{
+       D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
        list_del_init(&dentry->d_lru);
        dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
-       dentry->d_sb->s_nr_dentry_unused--;
-       dentry_stat.nr_unused--;
+       this_cpu_dec(nr_dentry_unused);
+}
+
+static void d_shrink_add(struct dentry *dentry, struct list_head *list)
+{
+       D_FLAG_VERIFY(dentry, 0);
+       list_add(&dentry->d_lru, list);
+       dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
+       this_cpu_inc(nr_dentry_unused);
 }
 
 /*
- * Remove a dentry with references from the LRU.
+ * These can only be called under the global LRU lock, ie during the
+ * callback for freeing the LRU list. "isolate" removes it from the
+ * LRU lists entirely, while shrink_move moves it to the indicated
+ * private list.
  */
-static void dentry_lru_del(struct dentry *dentry)
+static void d_lru_isolate(struct dentry *dentry)
 {
-       if (!list_empty(&dentry->d_lru)) {
-               spin_lock(&dcache_lru_lock);
-               __dentry_lru_del(dentry);
-               spin_unlock(&dcache_lru_lock);
-       }
+       D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+       dentry->d_flags &= ~DCACHE_LRU_LIST;
+       this_cpu_dec(nr_dentry_unused);
+       list_del_init(&dentry->d_lru);
 }
 
-static void dentry_lru_move_list(struct dentry *dentry, struct list_head *list)
+static void d_lru_shrink_move(struct dentry *dentry, struct list_head *list)
 {
-       spin_lock(&dcache_lru_lock);
-       if (list_empty(&dentry->d_lru)) {
-               dentry->d_flags |= DCACHE_LRU_LIST;
-               list_add_tail(&dentry->d_lru, list);
-               dentry->d_sb->s_nr_dentry_unused++;
-               dentry_stat.nr_unused++;
-       } else {
-               list_move_tail(&dentry->d_lru, list);
+       D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+       dentry->d_flags |= DCACHE_SHRINK_LIST;
+       list_move_tail(&dentry->d_lru, list);
+}
+
+/*
+ * dentry_lru_(add|del)_list) must be called with d_lock held.
+ */
+static void dentry_lru_add(struct dentry *dentry)
+{
+       if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
+               d_lru_add(dentry);
+}
+
+/*
+ * Remove a dentry with references from the LRU.
+ *
+ * If we are on the shrink list, then we can get to try_prune_one_dentry() and
+ * lose our last reference through the parent walk. In this case, we need to
+ * remove ourselves from the shrink list, not the LRU.
+ */
+static void dentry_lru_del(struct dentry *dentry)
+{
+       if (dentry->d_flags & DCACHE_LRU_LIST) {
+               if (dentry->d_flags & DCACHE_SHRINK_LIST)
+                       return d_shrink_del(dentry);
+               d_lru_del(dentry);
        }
-       spin_unlock(&dcache_lru_lock);
 }
 
 /**
@@ -474,7 +542,8 @@ EXPORT_SYMBOL(d_drop);
  * If ref is non-zero, then decrement the refcount too.
  * Returns dentry requiring refcount drop, or NULL if we're done.
  */
-static inline struct dentry *dentry_kill(struct dentry *dentry)
+static inline struct dentry *
+dentry_kill(struct dentry *dentry, int unlock_on_failure)
        __releases(dentry->d_lock)
 {
        struct inode *inode;
@@ -483,8 +552,10 @@ static inline struct dentry *dentry_kill(struct dentry *dentry)
        inode = dentry->d_inode;
        if (inode && !spin_trylock(&inode->i_lock)) {
 relock:
-               spin_unlock(&dentry->d_lock);
-               cpu_relax();
+               if (unlock_on_failure) {
+                       spin_unlock(&dentry->d_lock);
+                       cpu_relax();
+               }
                return dentry; /* try again with same dentry */
        }
        if (IS_ROOT(dentry))
@@ -567,7 +638,7 @@ repeat:
        return;
 
 kill_it:
-       dentry = dentry_kill(dentry);
+       dentry = dentry_kill(dentry, 1);
        if (dentry)
                goto repeat;
 }
@@ -787,12 +858,12 @@ EXPORT_SYMBOL(d_prune_aliases);
  *
  * This may fail if locks cannot be acquired no problem, just try again.
  */
-static void try_prune_one_dentry(struct dentry *dentry)
+static struct dentry * try_prune_one_dentry(struct dentry *dentry)
        __releases(dentry->d_lock)
 {
        struct dentry *parent;
 
-       parent = dentry_kill(dentry);
+       parent = dentry_kill(dentry, 0);
        /*
         * If dentry_kill returns NULL, we have nothing more to do.
         * if it returns the same dentry, trylocks failed. In either
@@ -804,17 +875,18 @@ static void try_prune_one_dentry(struct dentry *dentry)
         * fragmentation.
         */
        if (!parent)
-               return;
+               return NULL;
        if (parent == dentry)
-               return;
+               return dentry;
 
        /* Prune ancestors. */
        dentry = parent;
        while (dentry) {
                if (lockref_put_or_lock(&dentry->d_lockref))
-                       return;
-               dentry = dentry_kill(dentry);
+                       return NULL;
+               dentry = dentry_kill(dentry, 1);
        }
+       return NULL;
 }
 
 static void shrink_dentry_list(struct list_head *list)
@@ -826,83 +898,159 @@ static void shrink_dentry_list(struct list_head *list)
                dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
                if (&dentry->d_lru == list)
                        break; /* empty */
+
+               /*
+                * Get the dentry lock, and re-verify that the dentry is
+                * this on the shrinking list. If it is, we know that
+                * DCACHE_SHRINK_LIST and DCACHE_LRU_LIST are set.
+                */
                spin_lock(&dentry->d_lock);
                if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
                        spin_unlock(&dentry->d_lock);
                        continue;
                }
 
+               /*
+                * The dispose list is isolated and dentries are not accounted
+                * to the LRU here, so we can simply remove it from the list
+                * here regardless of whether it is referenced or not.
+                */
+               d_shrink_del(dentry);
+
                /*
                 * We found an inuse dentry which was not removed from
-                * the LRU because of laziness during lookup.  Do not free
-                * it - just keep it off the LRU list.
+                * the LRU because of laziness during lookup. Do not free it.
                 */
                if (dentry->d_lockref.count) {
-                       dentry_lru_del(dentry);
                        spin_unlock(&dentry->d_lock);
                        continue;
                }
-
                rcu_read_unlock();
 
-               try_prune_one_dentry(dentry);
+               /*
+                * If 'try_to_prune()' returns a dentry, it will
+                * be the same one we passed in, and d_lock will
+                * have been held the whole time, so it will not
+                * have been added to any other lists. We failed
+                * to get the inode lock.
+                *
+                * We just add it back to the shrink list.
+                */
+               dentry = try_prune_one_dentry(dentry);
 
                rcu_read_lock();
+               if (dentry) {
+                       d_shrink_add(dentry, list);
+                       spin_unlock(&dentry->d_lock);
+               }
        }
        rcu_read_unlock();
 }
 
+static enum lru_status
+dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
+{
+       struct list_head *freeable = arg;
+       struct dentry   *dentry = container_of(item, struct dentry, d_lru);
+
+
+       /*
+        * we are inverting the lru lock/dentry->d_lock here,
+        * so use a trylock. If we fail to get the lock, just skip
+        * it
+        */
+       if (!spin_trylock(&dentry->d_lock))
+               return LRU_SKIP;
+
+       /*
+        * Referenced dentries are still in use. If they have active
+        * counts, just remove them from the LRU. Otherwise give them
+        * another pass through the LRU.
+        */
+       if (dentry->d_lockref.count) {
+               d_lru_isolate(dentry);
+               spin_unlock(&dentry->d_lock);
+               return LRU_REMOVED;
+       }
+
+       if (dentry->d_flags & DCACHE_REFERENCED) {
+               dentry->d_flags &= ~DCACHE_REFERENCED;
+               spin_unlock(&dentry->d_lock);
+
+               /*
+                * The list move itself will be made by the common LRU code. At
+                * this point, we've dropped the dentry->d_lock but keep the
+                * lru lock. This is safe to do, since every list movement is
+                * protected by the lru lock even if both locks are held.
+                *
+                * This is guaranteed by the fact that all LRU management
+                * functions are intermediated by the LRU API calls like
+                * list_lru_add and list_lru_del. List movement in this file
+                * only ever occur through this functions or through callbacks
+                * like this one, that are called from the LRU API.
+                *
+                * The only exceptions to this are functions like
+                * shrink_dentry_list, and code that first checks for the
+                * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
+                * operating only with stack provided lists after they are
+                * properly isolated from the main list.  It is thus, always a
+                * local access.
+                */
+               return LRU_ROTATE;
+       }
+
+       d_lru_shrink_move(dentry, freeable);
+       spin_unlock(&dentry->d_lock);
+
+       return LRU_REMOVED;
+}
+
 /**
  * prune_dcache_sb - shrink the dcache
  * @sb: superblock
- * @count: number of entries to try to free
+ * @nr_to_scan : number of entries to try to free
+ * @nid: which node to scan for freeable entities
  *
- * Attempt to shrink the superblock dcache LRU by @count entries. This is
+ * Attempt to shrink the superblock dcache LRU by @nr_to_scan entries. This is
  * done when we need more memory an called from the superblock shrinker
  * function.
  *
  * This function may fail to free any resources if all the dentries are in
  * use.
  */
-void prune_dcache_sb(struct super_block *sb, int count)
+long prune_dcache_sb(struct super_block *sb, unsigned long nr_to_scan,
+                    int nid)
 {
-       struct dentry *dentry;
-       LIST_HEAD(referenced);
-       LIST_HEAD(tmp);
+       LIST_HEAD(dispose);
+       long freed;
 
-relock:
-       spin_lock(&dcache_lru_lock);
-       while (!list_empty(&sb->s_dentry_lru)) {
-               dentry = list_entry(sb->s_dentry_lru.prev,
-                               struct dentry, d_lru);
-               BUG_ON(dentry->d_sb != sb);
-
-               if (!spin_trylock(&dentry->d_lock)) {
-                       spin_unlock(&dcache_lru_lock);
-                       cpu_relax();
-                       goto relock;
-               }
+       freed = list_lru_walk_node(&sb->s_dentry_lru, nid, dentry_lru_isolate,
+                                      &dispose, &nr_to_scan);
+       shrink_dentry_list(&dispose);
+       return freed;
+}
 
-               if (dentry->d_flags & DCACHE_REFERENCED) {
-                       dentry->d_flags &= ~DCACHE_REFERENCED;
-                       list_move(&dentry->d_lru, &referenced);
-                       spin_unlock(&dentry->d_lock);
-               } else {
-                       list_move_tail(&dentry->d_lru, &tmp);
-                       dentry->d_flags |= DCACHE_SHRINK_LIST;
-                       spin_unlock(&dentry->d_lock);
-                       if (!--count)
-                               break;
-               }
-               cond_resched_lock(&dcache_lru_lock);
-       }
-       if (!list_empty(&referenced))
-               list_splice(&referenced, &sb->s_dentry_lru);
-       spin_unlock(&dcache_lru_lock);
+static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
+                                               spinlock_t *lru_lock, void *arg)
+{
+       struct list_head *freeable = arg;
+       struct dentry   *dentry = container_of(item, struct dentry, d_lru);
+
+       /*
+        * we are inverting the lru lock/dentry->d_lock here,
+        * so use a trylock. If we fail to get the lock, just skip
+        * it
+        */
+       if (!spin_trylock(&dentry->d_lock))
+               return LRU_SKIP;
 
-       shrink_dentry_list(&tmp);
+       d_lru_shrink_move(dentry, freeable);
+       spin_unlock(&dentry->d_lock);
+
+       return LRU_REMOVED;
 }
 
+
 /**
  * shrink_dcache_sb - shrink dcache for a superblock
  * @sb: superblock
@@ -912,16 +1060,17 @@ relock:
  */
 void shrink_dcache_sb(struct super_block *sb)
 {
-       LIST_HEAD(tmp);
+       long freed;
 
-       spin_lock(&dcache_lru_lock);
-       while (!list_empty(&sb->s_dentry_lru)) {
-               list_splice_init(&sb->s_dentry_lru, &tmp);
-               spin_unlock(&dcache_lru_lock);
-               shrink_dentry_list(&tmp);
-               spin_lock(&dcache_lru_lock);
-       }
-       spin_unlock(&dcache_lru_lock);
+       do {
+               LIST_HEAD(dispose);
+
+               freed = list_lru_walk(&sb->s_dentry_lru,
+                       dentry_lru_isolate_shrink, &dispose, UINT_MAX);
+
+               this_cpu_sub(nr_dentry_unused, freed);
+               shrink_dentry_list(&dispose);
+       } while (freed > 0);
 }
 EXPORT_SYMBOL(shrink_dcache_sb);
 
@@ -1182,14 +1331,6 @@ rename_retry:
  * list is non-empty and continue searching.
  */
 
-/**
- * have_submounts - check for mounts over a dentry
- * @parent: dentry to check.
- *
- * Return true if the parent or its subdirectories contain
- * a mount point
- */
-
 static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
 {
        int *ret = data;
@@ -1200,6 +1341,13 @@ static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
        return D_WALK_CONTINUE;
 }
 
+/**
+ * have_submounts - check for mounts over a dentry
+ * @parent: dentry to check.
+ *
+ * Return true if the parent or its subdirectories contain
+ * a mount point
+ */
 int have_submounts(struct dentry *parent)
 {
        int ret = 0;
@@ -1283,8 +1431,13 @@ static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
        if (dentry->d_lockref.count) {
                dentry_lru_del(dentry);
        } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
-               dentry_lru_move_list(dentry, &data->dispose);
-               dentry->d_flags |= DCACHE_SHRINK_LIST;
+               /*
+                * We can't use d_lru_shrink_move() because we
+                * need to get the global LRU lock and do the
+                * LRU accounting.
+                */
+               d_lru_del(dentry);
+               d_shrink_add(dentry, &data->dispose);
                data->found++;
                ret = D_WALK_NORETRY;
        }
@@ -1647,6 +1800,32 @@ struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
 
 EXPORT_SYMBOL(d_instantiate_unique);
 
+/**
+ * d_instantiate_no_diralias - instantiate a non-aliased dentry
+ * @entry: dentry to complete
+ * @inode: inode to attach to this dentry
+ *
+ * Fill in inode information in the entry.  If a directory alias is found, then
+ * return an error.  Together with d_materialise_unique() this guarantees that a
+ * directory inode may never have more than one alias.
+ */
+int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
+{
+       BUG_ON(!hlist_unhashed(&entry->d_alias));
+
+       spin_lock(&inode->i_lock);
+       if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
+               spin_unlock(&inode->i_lock);
+               return -EBUSY;
+       }
+       __d_instantiate(entry, inode);
+       spin_unlock(&inode->i_lock);
+       security_d_instantiate(entry, inode);
+
+       return 0;
+}
+EXPORT_SYMBOL(d_instantiate_no_diralias);
+
 struct dentry *d_make_root(struct inode *root_inode)
 {
        struct dentry *res = NULL;
@@ -2673,9 +2852,9 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen)
 
 /**
  * prepend_name - prepend a pathname in front of current buffer pointer
- * buffer: buffer pointer
- * buflen: allocated length of the buffer
- * name:   name string and length qstr structure
+ * @buffer: buffer pointer
+ * @buflen: allocated length of the buffer
+ * @name:   name string and length qstr structure
  *
  * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
  * make sure that either the old or the new name pointer and length are
@@ -2713,14 +2892,15 @@ static int prepend_name(char **buffer, int *buflen, struct qstr *name)
  * @buffer: pointer to the end of the buffer
  * @buflen: pointer to buffer length
  *
- * The function tries to write out the pathname without taking any lock other
- * than the RCU read lock to make sure that dentries won't go away. It only
- * checks the sequence number of the global rename_lock as any change in the
- * dentry's d_seq will be preceded by changes in the rename_lock sequence
- * number. If the sequence number had been change, it will restart the whole
- * pathname back-tracing sequence again. It performs a total of 3 trials of
- * lockless back-tracing sequences before falling back to take the
- * rename_lock.
+ * The function will first try to write out the pathname without taking any
+ * lock other than the RCU read lock to make sure that dentries won't go away.
+ * It only checks the sequence number of the global rename_lock as any change
+ * in the dentry's d_seq will be preceded by changes in the rename_lock
+ * sequence number. If the sequence number had been changed, it will restart
+ * the whole pathname back-tracing sequence again by taking the rename_lock.
+ * In this case, there is no need to take the RCU read lock as the recursive
+ * parent pointer references will keep the dentry chain alive as long as no
+ * rename operation is performed.
  */
 static int prepend_path(const struct path *path,
                        const struct path *root,
@@ -2868,6 +3048,16 @@ static int prepend_unreachable(char **buffer, int *buflen)
        return prepend(buffer, buflen, "(unreachable)", 13);
 }
 
+static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
+{
+       unsigned seq;
+
+       do {
+               seq = read_seqcount_begin(&fs->seq);
+               *root = fs->root;
+       } while (read_seqcount_retry(&fs->seq, seq));
+}
+
 /**
  * d_path - return the path of a dentry
  * @path: path to report
@@ -2900,13 +3090,15 @@ char *d_path(const struct path *path, char *buf, int buflen)
        if (path->dentry->d_op && path->dentry->d_op->d_dname)
                return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
 
-       get_fs_root(current->fs, &root);
+       rcu_read_lock();
+       get_fs_root_rcu(current->fs, &root);
        br_read_lock(&vfsmount_lock);
        error = path_with_deleted(path, &root, &res, &buflen);
        br_read_unlock(&vfsmount_lock);
+       rcu_read_unlock();
+
        if (error < 0)
                res = ERR_PTR(error);
-       path_put(&root);
        return res;
 }
 EXPORT_SYMBOL(d_path);
@@ -3014,6 +3206,18 @@ Elong:
        return ERR_PTR(-ENAMETOOLONG);
 }
 
+static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
+                                   struct path *pwd)
+{
+       unsigned seq;
+
+       do {
+               seq = read_seqcount_begin(&fs->seq);
+               *root = fs->root;
+               *pwd = fs->pwd;
+       } while (read_seqcount_retry(&fs->seq, seq));
+}
+
 /*
  * NOTE! The user-level library version returns a
  * character pointer. The kernel system call just
@@ -3036,23 +3240,25 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
 {
        int error;
        struct path pwd, root;
-       char *page = (char *) __get_free_page(GFP_USER);
+       char *page = __getname();
 
        if (!page)
                return -ENOMEM;
 
-       get_fs_root_and_pwd(current->fs, &root, &pwd);
+       rcu_read_lock();
+       get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
 
        error = -ENOENT;
        br_read_lock(&vfsmount_lock);
        if (!d_unlinked(pwd.dentry)) {
                unsigned long len;
-               char *cwd = page + PAGE_SIZE;
-               int buflen = PAGE_SIZE;
+               char *cwd = page + PATH_MAX;
+               int buflen = PATH_MAX;
 
                prepend(&cwd, &buflen, "\0", 1);
                error = prepend_path(&pwd, &root, &cwd, &buflen);
                br_read_unlock(&vfsmount_lock);
+               rcu_read_unlock();
 
                if (error < 0)
                        goto out;
@@ -3065,7 +3271,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
                }
 
                error = -ERANGE;
-               len = PAGE_SIZE + page - cwd;
+               len = PATH_MAX + page - cwd;
                if (len <= size) {
                        error = len;
                        if (copy_to_user(buf, cwd, len))
@@ -3073,12 +3279,11 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
                }
        } else {
                br_read_unlock(&vfsmount_lock);
+               rcu_read_unlock();
        }
 
 out:
-       path_put(&pwd);
-       path_put(&root);
-       free_page((unsigned long) page);
+       __putname(page);
        return error;
 }