There are members of task_struct which are only used by a given call chain to
pass arguments up and down the chain itself. They are logically thread-local
storage.
The patches later in the series want to have multiple calls pending for a given
task, though only one will be executing at a given time. By putting these
thread-local members of task_struct in a seperate storage structure we're able
to trivially swap them in and out as their calls are swapped in and out.
per_call_chain() doesn't have a terribly great name. It was chosen in the
spirit of per_cpu().
The storage was left inline in task_struct to avoid introducing indirection for
the vast majority of uses which will never have multiple calls executing in a
task.
I chose a few members of task_struct to migrate under per_call_chain() along
with the introduction as an example of what it looks like. These would be
seperate patches in a patch series that was suitable for merging.
diff -r b1128b48dc99 -r 26e278468209 fs/jbd/journal.c
--- a/fs/jbd/journal.c Fri Jan 12 20:00:03 2007 +0000
+++ b/fs/jbd/journal.c Mon Jan 29 15:36:13 2007 -0800
@@ -471,7 +471,7 @@ int journal_force_commit_nested(journal_
tid_t tid;
spin_lock(&journal->j_state_lock);
- if (journal->j_running_transaction && !current->journal_info) {
+ if (journal->j_running_transaction && !per_call_chain(journal_info)) {
transaction = journal->j_running_transaction;
__log_start_commit(journal, transaction->t_tid);
} else if (journal->j_committing_transaction)
diff -r b1128b48dc99 -r 26e278468209 fs/jbd/transaction.c
--- a/fs/jbd/transaction.c Fri Jan 12 20:00:03 2007 +0000
+++ b/fs/jbd/transaction.c Mon Jan 29 15:36:13 2007 -0800
@@ -279,12 +279,12 @@ handle_t *journal_start(journal_t *journ
if (!handle)
return ERR_PTR(-ENOMEM);
- current->journal_info = handle;
+ per_call_chain(journal_info) = handle;
err = start_this_handle(journal, handle);
if (err < 0) {
jbd_free_handle(handle);
- current->journal_info = NULL;
+ per_call_chain(journal_info) = NULL;
handle = ERR_PTR(err);
}
return handle;
@@ -1368,7 +1368,7 @@ int journal_stop(handle_t *handle)
} while (old_handle_count != transaction->t_handle_count);
}
- current->journal_info = NULL;
+ per_call_chain(journal_info) = NULL;
spin_lock(&journal->j_state_lock);
spin_lock(&transaction->t_handle_lock);
transaction->t_outstanding_credits -= handle->h_buffer_credits;
diff -r b1128b48dc99 -r 26e278468209 fs/namei.c
--- a/fs/namei.c Fri Jan 12 20:00:03 2007 +0000
+++ b/fs/namei.c Mon Jan 29 15:36:13 2007 -0800
@@ -628,20 +628,20 @@ static inline int do_follow_link(struct
static inline int do_follow_link(struct path *path, struct nameidata *nd)
{
int err = -ELOOP;
- if (current->link_count >= MAX_NESTED_LINKS)
+ if (per_call_chain(link_count) >= MAX_NESTED_LINKS)
goto loop;
- if (current->total_link_count >= 40)
+ if (per_call_chain(total_link_count) >= 40)
goto loop;
BUG_ON(nd->depth >= MAX_NESTED_LINKS);
cond_resched();
err = security_inode_follow_link(path->dentry, nd);
if (err)
goto loop;
- current->link_count++;
- current->total_link_count++;
+ per_call_chain(link_count)++;
+ per_call_chain(total_link_count)++;
nd->depth++;
err = __do_follow_link(path, nd);
- current->link_count--;
+ per_call_chain(link_count)--;
nd->depth--;
return err;
loop:
@@ -1025,7 +1025,7 @@ int fastcall link_path_walk(const char *
int fastcall path_walk(const char * name, struct nameidata *nd)
{
- current->total_link_count = 0;
+ per_call_chain(total_link_count) = 0;
return link_path_walk(name, nd);
}
@@ -1153,7 +1153,7 @@ static int fastcall do_path_lookup(int d
fput_light(file, fput_needed);
}
- current->total_link_count = 0;
+ per_call_chain(total_link_count) = 0;
retval = link_path_walk(name, nd);
out:
if (likely(retval == 0)) {
diff -r b1128b48dc99 -r 26e278468209 include/linux/init_task.h
--- a/include/linux/init_task.h Fri Jan 12 20:00:03 2007 +0000
+++ b/include/linux/init_task.h Mon Jan 29 15:36:13 2007 -0800
@@ -88,6 +88,11 @@ extern struct nsproxy init_nsproxy;
extern struct group_info init_groups;
+#define INIT_PER_CALL_CHAIN(tsk) \
+{ \
+ .journal_info = NULL, \
+}
+
/*
* INIT_TASK is used to set up the first task table, touch at
* your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -124,6 +129,7 @@ extern struct group_info init_groups;
.keep_capabilities = 0, \
.user = INIT_USER, \
.comm = "swapper", \
+ .per_call = INIT_PER_CALL_CHAIN(tsk), \
.thread = INIT_THREAD, \
.fs = &init_fs, \
.files = &init_files, \
@@ -135,7 +141,6 @@ extern struct group_info init_groups;
.signal = {{0}}}, \
.blocked = {{0}}, \
.alloc_lock = __SPIN_LOCK_UNLOCKED(tsk.alloc_lock), \
- .journal_info = NULL, \
.cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
.fs_excl = ATOMIC_INIT(0), \
.pi_lock = SPIN_LOCK_UNLOCKED, \
diff -r b1128b48dc99 -r 26e278468209 include/linux/jbd.h
--- a/include/linux/jbd.h Fri Jan 12 20:00:03 2007 +0000
+++ b/include/linux/jbd.h Mon Jan 29 15:36:13 2007 -0800
@@ -883,7 +883,7 @@ extern void __wait_on_journal (journal_
static inline handle_t *journal_current_handle(void)
{
- return current->journal_info;
+ return per_call_chain(journal_info);
}
/* The journaling code user interface:
diff -r b1128b48dc99 -r 26e278468209 include/linux/sched.h
--- a/include/linux/sched.h Fri Jan 12 20:00:03 2007 +0000
+++ b/include/linux/sched.h Mon Jan 29 15:36:13 2007 -0800
@@ -784,6 +784,20 @@ static inline void prefetch_stack(struct
static inline void prefetch_stack(struct task_struct *t) { }
#endif
+/*
+ * Members of this structure are used to pass arguments down call chains
+ * without specific arguments. Historically they lived on task_struct,
+ * putting them in one place gives us some flexibility. They're accessed
+ * with per_call_chain(name).
+ */
+struct per_call_chain_storage {
+ int link_count; /* number of links in one symlink */
+ int total_link_count; /* total links followed in a lookup */
+ void *journal_info; /* journalling filesystem info */
+};
+
+#define per_call_chain(foo) current->per_call.foo
+
struct audit_context; /* See audit.c */
struct mempolicy;
struct pipe_inode_info;
@@ -920,7 +934,7 @@ struct task_struct {
it with task_lock())
- initialized normally by flush_old_exec */
/* file system info */
- int link_count, total_link_count;
+ struct per_call_chain_storage per_call;
#ifdef CONFIG_SYSVIPC
/* ipc stuff */
struct sysv_sem sysvsem;
@@ -993,9 +1007,6 @@ struct task_struct {
struct held_lock held_locks[MAX_LOCK_DEPTH];
unsigned int lockdep_recursion;
#endif
-
-/* journalling filesystem info */
- void *journal_info;
/* VM state */
struct reclaim_state *reclaim_state;
-
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