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linuxkpi: Accept NULL as a value in linux_xarray

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Linux' XArray allows to store a NULL pointer as a value. `xa_load()`
would return NULL for both an unused index and an index set to NULL. But
it impacts `xa_alloc()` which needs to find the next available index.

However, our implementation relies on a radix tree (see `linux_radix.c`)
which does not accept NULL pointers as values. I'm not sure if this is a
limitation or a feature, so to work around this, a NULL value is
replaced by `NULL_VALUE`, an unlikely address, when we pass it to
linux_radix.

Reviewed by:	emaste, manu
Approved by:	emaste, manu
Differential Revision:	https://reviews.freebsd.org/D38543
This commit is contained in:
Jean-Sébastien Pédron 2023-02-11 11:12:08 +01:00
parent 364391a9bb
commit 3102ea3b15
No known key found for this signature in database
GPG key ID: 39E99761A5FD94CC
1 changed files with 37 additions and 1 deletions
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38
sys/compat/linuxkpi/common/src/linux_xarray.c
View file

@ -31,6 +31,18 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_pageout.h>
/*
* Linux' XArray allows to store a NULL pointer as a value. xa_load() would
* return NULL for both an unused index and an index set to NULL. But it
* impacts xa_alloc() which needs to find the next available index.
*
* However, our implementation relies on a radix tree (see `linux_radix.c`)
* which does not accept NULL pointers as values. I'm not sure this is a
* limitation or a feature, so to work around this, a NULL value is replaced by
* `NULL_VALUE`, an unlikely address, when we pass it to linux_radix.
*/
#define NULL_VALUE (void *)0x1
/*
* This function removes the element at the given index and returns
* the pointer to the removed element, if any.
@ -38,9 +50,15 @@ __FBSDID("$FreeBSD$");
void *
__xa_erase(struct xarray *xa, uint32_t index)
{
void *retval;
XA_ASSERT_LOCKED(xa);
return (radix_tree_delete(&xa->root, index));
retval = radix_tree_delete(&xa->root, index);
if (retval == NULL_VALUE)
retval = NULL;
return (retval);
}
void *
@ -68,6 +86,9 @@ xa_load(struct xarray *xa, uint32_t index)
retval = radix_tree_lookup(&xa->root, index);
xa_unlock(xa);
if (retval == NULL_VALUE)
retval = NULL;
return (retval);
}
@ -109,6 +130,8 @@ __xa_alloc(struct xarray *xa, uint32_t *pindex, void *ptr, uint32_t mask, gfp_t
MPASS((mask & (mask + 1)) == 0);
*pindex = (xa->flags & XA_FLAGS_ALLOC1) != 0 ? 1 : 0;
if (ptr == NULL)
ptr = NULL_VALUE;
retry:
retval = radix_tree_insert(&xa->root, *pindex, ptr);
@ -137,6 +160,9 @@ xa_alloc(struct xarray *xa, uint32_t *pindex, void *ptr, uint32_t mask, gfp_t gf
{
int retval;
if (ptr == NULL)
ptr = NULL_VALUE;
xa_lock(xa);
retval = __xa_alloc(xa, pindex, ptr, mask, gfp);
xa_unlock(xa);
@ -166,6 +192,8 @@ __xa_alloc_cyclic(struct xarray *xa, uint32_t *pindex, void *ptr, uint32_t mask,
MPASS((mask & (mask + 1)) == 0);
*pnext_index = (xa->flags & XA_FLAGS_ALLOC1) != 0 ? 1 : 0;
if (ptr == NULL)
ptr = NULL_VALUE;
retry:
retval = radix_tree_insert(&xa->root, *pnext_index, ptr);
@ -220,6 +248,8 @@ __xa_insert(struct xarray *xa, uint32_t index, void *ptr, gfp_t gfp)
int retval;
XA_ASSERT_LOCKED(xa);
if (ptr == NULL)
ptr = NULL_VALUE;
retry:
retval = radix_tree_insert(&xa->root, index, ptr);
@ -262,11 +292,15 @@ __xa_store(struct xarray *xa, uint32_t index, void *ptr, gfp_t gfp)
int retval;
XA_ASSERT_LOCKED(xa);
if (ptr == NULL)
ptr = NULL_VALUE;
retry:
retval = radix_tree_store(&xa->root, index, &ptr);
switch (retval) {
case 0:
if (ptr == NULL_VALUE)
ptr = NULL;
break;
case -ENOMEM:
if (likely(gfp & M_WAITOK)) {
@ -374,6 +408,8 @@ __xa_next(struct xarray *xa, unsigned long *pindex, bool not_first)
found = radix_tree_iter_find(&xa->root, &iter, &ppslot);
if (likely(found)) {
retval = *ppslot;
if (retval == NULL_VALUE)
retval = NULL;
*pindex = iter.index;
} else {
retval = NULL;