lkml.org 
[lkml]   [2016]   [Oct]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC v2 PATCH] mm/percpu.c: fix panic triggered by BUG_ON() falsely
Date
From: zijun_hu <zijun_hu@htc.com>

as shown by pcpu_build_alloc_info(), the number of units within a percpu
group is educed by rounding up the number of CPUs within the group to
@upa boundary, therefore, the number of CPUs isn't equal to the units's
if it isn't aligned to @upa normally. however, pcpu_page_first_chunk()
uses BUG_ON() to assert one number is equal the other roughly, so a panic
is maybe triggered by the BUG_ON() falsely.

in order to fix this issue, the number of CPUs is rounded up then compared
with units's, the BUG_ON() is replaced by warning and returning error code
as well to keep system alive as much as possible.

Signed-off-by: zijun_hu <zijun_hu@htc.com>
---
Changes in v2:
- fix build error

mm/percpu.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 32e2d8d128c1..ab1186c68ab6 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2095,6 +2095,8 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
size_t pages_size;
struct page **pages;
int unit, i, j, rc;
+ int upa;
+ int nr_g0_units;

snprintf(psize_str, sizeof(psize_str), "%luK", PAGE_SIZE >> 10);

@@ -2102,7 +2104,12 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
if (IS_ERR(ai))
return PTR_ERR(ai);
BUG_ON(ai->nr_groups != 1);
- BUG_ON(ai->groups[0].nr_units != num_possible_cpus());
+ upa = ai->alloc_size/ai->unit_size;
+ nr_g0_units = roundup(num_possible_cpus(), upa);
+ if (unlikely(WARN_ON(ai->groups[0].nr_units != nr_g0_units))) {
+ pcpu_free_alloc_info(ai);
+ return -EINVAL;
+ }

unit_pages = ai->unit_size >> PAGE_SHIFT;

@@ -2113,21 +2120,22 @@ int __init pcpu_page_first_chunk(size_t reserved_size,

/* allocate pages */
j = 0;
- for (unit = 0; unit < num_possible_cpus(); unit++)
+ for (unit = 0; unit < num_possible_cpus(); unit++) {
+ unsigned int cpu = ai->groups[0].cpu_map[unit];
for (i = 0; i < unit_pages; i++) {
- unsigned int cpu = ai->groups[0].cpu_map[unit];
void *ptr;

ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE);
if (!ptr) {
pr_warn("failed to allocate %s page for cpu%u\n",
- psize_str, cpu);
+ psize_str, cpu);
goto enomem;
}
/* kmemleak tracks the percpu allocations separately */
kmemleak_free(ptr);
pages[j++] = virt_to_page(ptr);
}
+ }

/* allocate vm area, map the pages and copy static data */
vm.flags = VM_ALLOC;
--
1.9.1
\
 
 \ /
  Last update: 2016-10-11 16:01    [W:0.050 / U:15.628 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site