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Subject[PATCH] cma: don't quit at first error when activating reserved areas
Date
The routine cma_init_reserved_areas is designed to activate all
reserved cma areas. It quits when it first encounters an error.
This can leave some areas in a state where they are reserved but
not activated. There is no feedback to code which performed the
reservation. Attempting to allocate memory from areas in such a
state will result in a BUG.

Modify cma_init_reserved_areas to always attempt to activate all
areas. The called routine, cma_activate_area is responsible for
leaving the area in a valid state. No one is making active use
of returned error codes, so change the routine to void.

How to reproduce: This example uses kernelcore, hugetlb and cma
as an easy way to reproduce. However, this is a more general cma
issue.

Two node x86 VM 16GB total, 8GB per node
Kernel command line parameters, kernelcore=4G hugetlb_cma=8G
Related boot time messages,
hugetlb_cma: reserve 8192 MiB, up to 4096 MiB per node
cma: Reserved 4096 MiB at 0x0000000100000000
hugetlb_cma: reserved 4096 MiB on node 0
cma: Reserved 4096 MiB at 0x0000000300000000
hugetlb_cma: reserved 4096 MiB on node 1
cma: CMA area hugetlb could not be activated

# echo 8 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
...
Call Trace:
bitmap_find_next_zero_area_off+0x51/0x90
cma_alloc+0x1a5/0x310
alloc_fresh_huge_page+0x78/0x1a0
alloc_pool_huge_page+0x6f/0xf0
set_max_huge_pages+0x10c/0x250
nr_hugepages_store_common+0x92/0x120
? __kmalloc+0x171/0x270
kernfs_fop_write+0xc1/0x1a0
vfs_write+0xc7/0x1f0
ksys_write+0x5f/0xe0
do_syscall_64+0x4d/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: c64be2bb1c6e ("drivers: add Contiguous Memory Allocator")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: <stable@vger.kernel.org>
---
mm/cma.c | 23 +++++++++--------------
1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 26ecff818881..0963c0f9c502 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -93,17 +93,15 @@ static void cma_clear_bitmap(struct cma *cma, unsigned long pfn,
mutex_unlock(&cma->lock);
}

-static int __init cma_activate_area(struct cma *cma)
+static void __init cma_activate_area(struct cma *cma)
{
unsigned long base_pfn = cma->base_pfn, pfn = base_pfn;
unsigned i = cma->count >> pageblock_order;
struct zone *zone;

cma->bitmap = bitmap_zalloc(cma_bitmap_maxno(cma), GFP_KERNEL);
- if (!cma->bitmap) {
- cma->count = 0;
- return -ENOMEM;
- }
+ if (!cma->bitmap)
+ goto out_error;

WARN_ON_ONCE(!pfn_valid(pfn));
zone = page_zone(pfn_to_page(pfn));
@@ -133,25 +131,22 @@ static int __init cma_activate_area(struct cma *cma)
spin_lock_init(&cma->mem_head_lock);
#endif

- return 0;
+ return;

not_in_zone:
- pr_err("CMA area %s could not be activated\n", cma->name);
bitmap_free(cma->bitmap);
+out_error:
cma->count = 0;
- return -EINVAL;
+ pr_err("CMA area %s could not be activated\n", cma->name);
+ return;
}

static int __init cma_init_reserved_areas(void)
{
int i;

- for (i = 0; i < cma_area_count; i++) {
- int ret = cma_activate_area(&cma_areas[i]);
-
- if (ret)
- return ret;
- }
+ for (i = 0; i < cma_area_count; i++)
+ cma_activate_area(&cma_areas[i]);

return 0;
}
--
2.25.4
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