fs: dcache avoid starvation in dcache multi-step operations
Long lived dcache "multi-step" operations which retry on rename seq can
be starved with a lot of rename activity. If they fail after the 1st pass,
take the rename_lock for writing to avoid further starvation.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/fs/dcache.c b/fs/dcache.c
index 0dbae053b..bf6294a 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -973,10 +973,11 @@
struct dentry *this_parent;
struct list_head *next;
unsigned seq;
+ int locked = 0;
-rename_retry:
- this_parent = parent;
seq = read_seqbegin(&rename_lock);
+again:
+ this_parent = parent;
if (d_mountpoint(parent))
goto positive;
@@ -1021,7 +1022,7 @@
/* might go back up the wrong parent if we have had a rename
* or deletion */
if (this_parent != child->d_parent ||
- read_seqretry(&rename_lock, seq)) {
+ (!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
goto rename_retry;
@@ -1031,13 +1032,22 @@
goto resume;
}
spin_unlock(&this_parent->d_lock);
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
return 0; /* No mount points found in tree */
positive:
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
return 1;
+
+rename_retry:
+ locked = 1;
+ write_seqlock(&rename_lock);
+ goto again;
}
EXPORT_SYMBOL(have_submounts);
@@ -1061,11 +1071,11 @@
struct list_head *next;
unsigned seq;
int found = 0;
+ int locked = 0;
-rename_retry:
- this_parent = parent;
seq = read_seqbegin(&rename_lock);
-
+again:
+ this_parent = parent;
spin_lock(&this_parent->d_lock);
repeat:
next = this_parent->d_subdirs.next;
@@ -1127,7 +1137,7 @@
/* might go back up the wrong parent if we have had a rename
* or deletion */
if (this_parent != child->d_parent ||
- read_seqretry(&rename_lock, seq)) {
+ (!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
goto rename_retry;
@@ -1138,9 +1148,18 @@
}
out:
spin_unlock(&this_parent->d_lock);
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
return found;
+
+rename_retry:
+ if (found)
+ return found;
+ locked = 1;
+ write_seqlock(&rename_lock);
+ goto again;
}
/**
@@ -2655,10 +2674,11 @@
struct dentry *this_parent;
struct list_head *next;
unsigned seq;
+ int locked = 0;
-rename_retry:
- this_parent = root;
seq = read_seqbegin(&rename_lock);
+again:
+ this_parent = root;
spin_lock(&this_parent->d_lock);
repeat:
next = this_parent->d_subdirs.next;
@@ -2703,7 +2723,7 @@
/* might go back up the wrong parent if we have had a rename
* or deletion */
if (this_parent != child->d_parent ||
- read_seqretry(&rename_lock, seq)) {
+ (!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
goto rename_retry;
@@ -2713,8 +2733,16 @@
goto resume;
}
spin_unlock(&this_parent->d_lock);
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
+ return;
+
+rename_retry:
+ locked = 1;
+ write_seqlock(&rename_lock);
+ goto again;
}
/**