From: Hugh Dickins <hugh@veritas.com>
Nick has tracked scheduling-while-atomic errors to shmem's fragile kmap
avoidance: the root error appears to lie deeper, but rework that fragility.
Plus I've been indicted for war crimes at the end of shmem_swp_entry: my
apologia scorned, so now hide the evidence.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/mm/shmem.c | 42 +++++++++++++++++++-----------------------
1 files changed, 19 insertions(+), 23 deletions(-)
diff -puN mm/shmem.c~tmpfs-scheduling-while-atomic-fix mm/shmem.c
--- 25/mm/shmem.c~tmpfs-scheduling-while-atomic-fix Thu Jul 8 16:05:44 2004
+++ 25-akpm/mm/shmem.c Thu Jul 8 16:05:44 2004
@@ -105,22 +105,24 @@ static inline void shmem_dir_unmap(struc
static swp_entry_t *shmem_swp_map(struct page *page)
{
+ return (swp_entry_t *)kmap_atomic(page, KM_USER1);
+}
+
+static inline void shmem_swp_balance_unmap(void)
+{
/*
- * We have to avoid the unconditional inc_preempt_count()
- * in kmap_atomic(), since shmem_swp_unmap() will also be
- * applied to the low memory addresses within i_direct[].
- * PageHighMem and high_memory tests are good for all arches
- * and configs: highmem_start_page and FIXADDR_START are not.
+ * When passing a pointer to an i_direct entry, to code which
+ * also handles indirect entries and so will shmem_swp_unmap,
+ * we must arrange for the preempt count to remain in balance.
+ * What kmap_atomic of a lowmem page does depends on config
+ * and architecture, so pretend to kmap_atomic some lowmem page.
*/
- return PageHighMem(page)?
- (swp_entry_t *)kmap_atomic(page, KM_USER1):
- (swp_entry_t *)page_address(page);
+ (void) kmap_atomic(ZERO_PAGE(0), KM_USER1);
}
static inline void shmem_swp_unmap(swp_entry_t *entry)
{
- if (entry >= (swp_entry_t *)high_memory)
- kunmap_atomic(entry, KM_USER1);
+ kunmap_atomic(entry, KM_USER1);
}
static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
@@ -263,8 +265,10 @@ static swp_entry_t *shmem_swp_entry(stru
struct page **dir;
struct page *subdir;
- if (index < SHMEM_NR_DIRECT)
+ if (index < SHMEM_NR_DIRECT) {
+ shmem_swp_balance_unmap();
return info->i_direct+index;
+ }
if (!info->i_indirect) {
if (page) {
info->i_indirect = *page;
@@ -306,17 +310,7 @@ static swp_entry_t *shmem_swp_entry(stru
*page = NULL;
}
shmem_dir_unmap(dir);
-
- /*
- * With apologies... caller shmem_swp_alloc passes non-NULL
- * page (though perhaps NULL *page); and now we know that this
- * indirect page has been allocated, we can shortcut the final
- * kmap if we know it contains no swap entries, as is commonly
- * the case: return pointer to a 0 which doesn't need kmapping.
- */
- return (page && !subdir->nr_swapped)?
- (swp_entry_t *)&subdir->nr_swapped:
- shmem_swp_map(subdir) + offset;
+ return shmem_swp_map(subdir) + offset;
}
static void shmem_swp_set(struct shmem_inode_info *info, swp_entry_t *entry, unsigned long value)
@@ -650,8 +644,10 @@ static int shmem_unuse_inode(struct shme
if (size > SHMEM_NR_DIRECT)
size = SHMEM_NR_DIRECT;
offset = shmem_find_swp(entry, ptr, ptr+size);
- if (offset >= 0)
+ if (offset >= 0) {
+ shmem_swp_balance_unmap();
goto found;
+ }
if (!info->i_indirect)
goto lost2;
/* we might be racing with shmem_truncate */
_