Eric Lee / smarc-ti-linux-kernel

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Commit 855ef0dec7271ff7be7381feaaf3f4aed80bd503

Authored by Oleg Nesterov
Committed by Benjamin LaHaise
1 parent 4b70ac5fd9
Exists in ti-lsk-linux-4.1.y and in 10 other branches dlt-processor-sdk-linux-03.00.00.04, processor-sdk-linux-02.00.01, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04

aio: kill the misleading rcu read locks in ioctx_add_table() and kill_ioctx() 

ioctx_add_table() is the writer, it does not need rcu_read_lock() to
protect ->ioctx_table. It relies on mm->ioctx_lock and rcu locks just
add the confusion.

And it doesn't need rcu_dereference() by the same reason, it must see
any updates previously done under the same ->ioctx_lock. We could use
rcu_dereference_protected() but the patch uses rcu_dereference_raw(),
the function is simple enough.

The same for kill_ioctx(), although it does not update the pointer.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>

Showing 1 changed file with 3 additions and 11 deletions Side-by-side Diff

... ... @@ -554,8 +554,7 @@
554 554 struct aio_ring *ring;
555 555  
556 556 spin_lock(&mm->ioctx_lock);
557   - rcu_read_lock();
558   - table = rcu_dereference(mm->ioctx_table);
  557 + table = rcu_dereference_raw(mm->ioctx_table);
559 558  
560 559 while (1) {
561 560 if (table)
... ... @@ -563,7 +562,6 @@
563 562 if (!table->table[i]) {
564 563 ctx->id = i;
565 564 table->table[i] = ctx;
566   - rcu_read_unlock();
567 565 spin_unlock(&mm->ioctx_lock);
568 566  
569 567 /* While kioctx setup is in progress,
... ... @@ -577,8 +575,6 @@
577 575 }
578 576  
579 577 new_nr = (table ? table->nr : 1) * 4;
580   -
581   - rcu_read_unlock();
582 578 spin_unlock(&mm->ioctx_lock);
583 579  
584 580 table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
... ... @@ -589,8 +585,7 @@
589 585 table->nr = new_nr;
590 586  
591 587 spin_lock(&mm->ioctx_lock);
592   - rcu_read_lock();
593   - old = rcu_dereference(mm->ioctx_table);
  588 + old = rcu_dereference_raw(mm->ioctx_table);
594 589  
595 590 if (!old) {
596 591 rcu_assign_pointer(mm->ioctx_table, table);
597 592  
... ... @@ -737,12 +732,9 @@
737 732  
738 733  
739 734 spin_lock(&mm->ioctx_lock);
740   - rcu_read_lock();
741   - table = rcu_dereference(mm->ioctx_table);
742   -
  735 + table = rcu_dereference_raw(mm->ioctx_table);
743 736 WARN_ON(ctx != table->table[ctx->id]);
744 737 table->table[ctx->id] = NULL;
745   - rcu_read_unlock();
746 738 spin_unlock(&mm->ioctx_lock);
747 739  
748 740 /* percpu_ref_kill() will do the necessary call_rcu() */