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xarray: Add xa_reserve and xa_release

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This function reserves a slot in the XArray for users which need
to acquire multiple locks before storing their entry in the tree and
so cannot use a plain xa_store().

Signed-off-by: Matthew Wilcox <willy@infradead.org>
This commit is contained in:
Matthew Wilcox 2018-10-01 14:54:59 -04:00
parent 2264f5132f
commit 9f14d4f1f1
4 changed files with 125 additions and 2 deletions
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47
lib/xarray.c
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@ -1266,6 +1266,8 @@ void *xa_load(struct xarray *xa, unsigned long index)
rcu_read_lock();
do {
entry = xas_load(&xas);
if (xa_is_zero(entry))
entry = NULL;
} while (xas_retry(&xas, entry));
rcu_read_unlock();
@ -1275,6 +1277,8 @@ EXPORT_SYMBOL(xa_load);
static void *xas_result(struct xa_state *xas, void *curr)
{
if (xa_is_zero(curr))
return NULL;
XA_NODE_BUG_ON(xas->xa_node, xa_is_internal(curr));
if (xas_error(xas))
curr = xas->xa_node;
@ -1394,6 +1398,8 @@ void *xa_cmpxchg(struct xarray *xa, unsigned long index,
do {
xas_lock(&xas);
curr = xas_load(&xas);
if (curr == XA_ZERO_ENTRY)
curr = NULL;
if (curr == old)
xas_store(&xas, entry);
xas_unlock(&xas);
@ -1430,6 +1436,8 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
do {
curr = xas_load(&xas);
if (curr == XA_ZERO_ENTRY)
curr = NULL;
if (curr == old)
xas_store(&xas, entry);
} while (__xas_nomem(&xas, gfp));
@ -1438,6 +1446,43 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
}
EXPORT_SYMBOL(__xa_cmpxchg);
/**
* xa_reserve() - Reserve this index in the XArray.
* @xa: XArray.
* @index: Index into array.
* @gfp: Memory allocation flags.
*
* Ensures there is somewhere to store an entry at @index in the array.
* If there is already something stored at @index, this function does
* nothing. If there was nothing there, the entry is marked as reserved.
* Loads from @index will continue to see a %NULL pointer until a
* subsequent store to @index.
*
* If you do not use the entry that you have reserved, call xa_release()
* or xa_erase() to free any unnecessary memory.
*
* Context: Process context. Takes and releases the xa_lock, IRQ or BH safe
* if specified in XArray flags. May sleep if the @gfp flags permit.
* Return: 0 if the reservation succeeded or -ENOMEM if it failed.
*/
int xa_reserve(struct xarray *xa, unsigned long index, gfp_t gfp)
{
XA_STATE(xas, xa, index);
unsigned int lock_type = xa_lock_type(xa);
void *curr;
do {
xas_lock_type(&xas, lock_type);
curr = xas_load(&xas);
if (!curr)
xas_store(&xas, XA_ZERO_ENTRY);
xas_unlock_type(&xas, lock_type);
} while (xas_nomem(&xas, gfp));
return xas_error(&xas);
}
EXPORT_SYMBOL(xa_reserve);
/**
* __xa_set_mark() - Set this mark on this entry while locked.
* @xa: XArray.
@ -1797,6 +1842,8 @@ void xa_dump_entry(const void *entry, unsigned long index, unsigned long shift)
pr_cont("retry (%ld)\n", xa_to_internal(entry));
else if (xa_is_sibling(entry))
pr_cont("sibling (slot %ld)\n", xa_to_sibling(entry));
else if (xa_is_zero(entry))
pr_cont("zero (%ld)\n", xa_to_internal(entry));
else
pr_cont("UNKNOWN ENTRY (%px)\n", entry);
}