2022-09-04 15:46:32

by Qiujun Huang

Subject: [PATCH] pstore/zone: Use GFP_ATOMIC to allocate zone buffer

There is a case found when triggering a panic_on_oom, pstore fails to dump
kmsg. Because psz_kmsg_write_record can't get the new buffer.

Handle this by using GFP_ATOMIC to allocate a buffer at lower watermark.

Signed-off-by: Qiujun Huang <[email protected]>
---
fs/pstore/zone.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pstore/zone.c b/fs/pstore/zone.c
index 017d0d4ad329..2770746bb7aa 100644
--- a/fs/pstore/zone.c
+++ b/fs/pstore/zone.c
@@ -761,7 +761,7 @@ static inline int notrace
psz_kmsg_write_record(struct psz_context *cxt,
/* avoid destroying old data, allocate a new one */
len = zone->buffer_size + sizeof(*zone->buffer);
zone->oldbuf = zone->buffer;
- zone->buffer = kzalloc(len, GFP_KERNEL);
+ zone->buffer = kzalloc(len, GFP_ATOMIC);
if (!zone->buffer) {
zone->buffer = zone->oldbuf;
return -ENOMEM;
--
2.25.1

2022-09-06 20:59:51

by Kees Cook

Subject: Re: [PATCH] pstore/zone: Use GFP_ATOMIC to allocate zone buffer

On Sun, Sep 04, 2022 at 11:17:13PM +0800, Qiujun Huang wrote:
> There is a case found when triggering a panic_on_oom, pstore fails to dump
> kmsg. Because psz_kmsg_write_record can't get the new buffer.
>
> Handle this by using GFP_ATOMIC to allocate a buffer at lower watermark.
>
> Signed-off-by: Qiujun Huang <[email protected]>
> ---
> fs/pstore/zone.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/pstore/zone.c b/fs/pstore/zone.c
> index 017d0d4ad329..2770746bb7aa 100644
> --- a/fs/pstore/zone.c
> +++ b/fs/pstore/zone.c
> @@ -761,7 +761,7 @@ static inline int notrace
> psz_kmsg_write_record(struct psz_context *cxt,
> /* avoid destroying old data, allocate a new one */
> len = zone->buffer_size + sizeof(*zone->buffer);
> zone->oldbuf = zone->buffer;
> - zone->buffer = kzalloc(len, GFP_KERNEL);
> + zone->buffer = kzalloc(len, GFP_ATOMIC);
> if (!zone->buffer) {
> zone->buffer = zone->oldbuf;
> return -ENOMEM;

This patch appears to be whitespace damaged, but I've manually applied
it. Thank you!

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=for-next/pstore&id=27001e611bb642287eddf93227bd72d295a35453

--
Kees Cook