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Subject[RESEND PATCH 1/2] aio: simplify fetching ioctx_table pointer from, mm_struct
Using rcu_dereference_protected() rather than the "rcu_read_lock-->
rcu_dereference-->rcu_read_unlock" group to simplify fetching the
ioctx_table pointer in ioctx_add_table and kill_ioctx, because it
is protected by the ioctx_lock.
And in the exit_aio(), there are no other users manipulating ioctx_table
at this stage, so we can use rcu_access_pointer directly.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
---
fs/aio.c | 42 ++++++++++++++++--------------------------
1 files changed, 16 insertions(+), 26 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 062a5f6..7eaa631 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -544,8 +544,8 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
struct aio_ring *ring;

spin_lock(&mm->ioctx_lock);
- rcu_read_lock();
- table = rcu_dereference(mm->ioctx_table);
+ table = rcu_dereference_protected(mm->ioctx_table,
+ lockdep_is_held(&mm->ioctx_lock));

while (1) {
if (table)
@@ -553,7 +553,6 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
if (!table->table[i]) {
ctx->id = i;
table->table[i] = ctx;
- rcu_read_unlock();
spin_unlock(&mm->ioctx_lock);

ring = kmap_atomic(ctx->ring_pages[0]);
@@ -564,7 +563,6 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)

new_nr = (table ? table->nr : 1) * 4;

- rcu_read_unlock();
spin_unlock(&mm->ioctx_lock);

table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
@@ -575,8 +573,8 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
table->nr = new_nr;

spin_lock(&mm->ioctx_lock);
- rcu_read_lock();
- old = rcu_dereference(mm->ioctx_table);
+ old = rcu_dereference_protected(mm->ioctx_table,
+ lockdep_is_held(&mm->ioctx_lock));

if (!old) {
rcu_assign_pointer(mm->ioctx_table, table);
@@ -711,12 +709,11 @@ static void kill_ioctx(struct mm_struct *mm, struct kioctx *ctx)
struct kioctx_table *table;

spin_lock(&mm->ioctx_lock);
- rcu_read_lock();
- table = rcu_dereference(mm->ioctx_table);
+ table = rcu_dereference_protected(mm->ioctx_table,
+ lockdep_is_held(&mm->ioctx_lock));

WARN_ON(ctx != table->table[ctx->id]);
table->table[ctx->id] = NULL;
- rcu_read_unlock();
spin_unlock(&mm->ioctx_lock);

/* percpu_ref_kill() will do the necessary call_rcu() */
@@ -765,27 +762,17 @@ EXPORT_SYMBOL(wait_on_sync_kiocb);
void exit_aio(struct mm_struct *mm)
{
struct kioctx_table *table;
- struct kioctx *ctx;
unsigned i = 0;

- while (1) {
- rcu_read_lock();
- table = rcu_dereference(mm->ioctx_table);
-
- do {
- if (!table || i >= table->nr) {
- rcu_read_unlock();
- rcu_assign_pointer(mm->ioctx_table, NULL);
- if (table)
- kfree(table);
- return;
- }
-
- ctx = table->table[i++];
- } while (!ctx);
+ table = rcu_access_pointer(mm->ioctx_table);
+ if (!table)
+ return;

- rcu_read_unlock();
+ while (i < table->nr) {
+ struct kioctx *ctx = table->table[i++];

+ if (!ctx)
+ continue;
/*
* We don't need to bother with munmap() here -
* exit_mmap(mm) is coming and it'll unmap everything.
@@ -798,6 +785,9 @@ void exit_aio(struct mm_struct *mm)

kill_ioctx(mm, ctx);
}
+
+ rcu_assign_pointer(mm->ioctx_table, NULL);
+ kfree(table);
}

static void put_reqs_available(struct kioctx *ctx, unsigned nr)
--
1.7.7


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