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locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe

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This is the temporary ugly hack which will be reverted later. We only
need it to ensure that the next patch will not break "change sb_writers
to use percpu_rw_semaphore" patches routed via the VFS tree.

The alloc_super()->destroy_super() error path assumes that it is safe
to call percpu_free_rwsem() after kzalloc() without percpu_init_rwsem(),
so let's not disappoint it.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Oleg Nesterov 2015-08-21 19:42:55 +02:00 committed by Paul E. McKenney
parent 07899a6e5f
commit 95b19f684c
1 changed files with 7 additions and 0 deletions
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7
kernel/locking/percpu-rwsem.c
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@ -26,6 +26,13 @@ EXPORT_SYMBOL_GPL(__percpu_init_rwsem);
void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
{
/*
* XXX: temporary kludge. The error path in alloc_super()
* assumes that percpu_free_rwsem() is safe after kzalloc().
*/
if (!brw->fast_read_ctr)
return;
free_percpu(brw->fast_read_ctr);
brw->fast_read_ctr = NULL; /* catch use after free bugs */
}