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mm/huge_memory: Fix xarray node memory leak 

If xas_split_alloc() fails to allocate the necessary nodes to complete the
xarray entry split, it sets the xa_state to -ENOMEM, which xas_nomem()
then interprets as "Please allocate more memory", not as "Please free
any unnecessary memory" (which was the intended outcome).  It's confusing
to use xas_nomem() to free memory in this context, so call xas_destroy()
instead.

Reported-by: syzbot+9e27a75a8c24f3fe75c1@syzkaller.appspotmail.com
Fixes: 6b24ca4a1a ("mm: Use multi-index entries in the page cache")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2022-06-08 15:18:34 -04:00
parent dcfa24ba68
commit 69a37a8ba1
3 changed files with 5 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/xarray.h
View File

@ -1508,6 +1508,7 @@ void *xas_find_marked(struct xa_state *, unsigned long max, xa_mark_t);
void xas_init_marks(const struct xa_state *);
bool xas_nomem(struct xa_state *, gfp_t);
void xas_destroy(struct xa_state *);
void xas_pause(struct xa_state *);
void xas_create_range(struct xa_state *);

5
lib/xarray.c
View File

@ -264,9 +264,10 @@ static void xa_node_free(struct xa_node *node)
* xas_destroy() - Free any resources allocated during the XArray operation.
* @xas: XArray operation state.
*
* This function is now internal-only.
* Most users will not need to call this function; it is called for you
* by xas_nomem().
*/
static void xas_destroy(struct xa_state *xas)
void xas_destroy(struct xa_state *xas)
{
struct xa_node *next, *node = xas->xa_alloc;

3
mm/huge_memory.c
View File

@ -2672,8 +2672,7 @@ out_unlock:
if (mapping)
i_mmap_unlock_read(mapping);
out:
/* Free any memory we didn't use */
xas_nomem(&xas, 0);
xas_destroy(&xas);
count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
return ret;
}