[Crash-utility] [PATCH v2] Fix kmem failing to print task context when address is vmalloced stack

[lijiang]

Hi, Tao
Thank you for the fix.
On Thu, Aug 25, 2022 at 8:00 PM <crash-utility-request at redhat.com> wrote:

> Date: Thu, 25 Aug 2022 14:42:45 +0800
> From: Tao Liu <ltao at redhat.com>
> To: crash-utility at redhat.com
> Subject: [Crash-utility] [PATCH v2] Fix kmem failing to print task
>         context when address is vmalloced stack
> Message-ID: <20220825064243.71447-1-ltao at redhat.com>
> Content-Type: text/plain; charset="US-ASCII"; x-default=true
>
> When kernel enabled CONFIG_VMAP_STACK, stack can be allocated to
> vmalloced area. Currently crash didn't handle the case, as a result,
> kmem will not print the task context as expected. This patch fix the
> bug by checking if the address is a vmalloced stack first.
>
> Before:
>     crash> kmem ffffb7efce9bbe28
>        VMAP_AREA         VM_STRUCT                 ADDRESS RANGE
>       SIZE
>     ffff94eb9102c640  ffff94eb9102b140  ffffb7efce9b8000 -
> ffffb7efce9bd000    20480
>
>           PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
>     ffffdd28220dc000 1883700000                0        0  1 50000000000000
>
> After:
>     crash> kmem ffffb7efce9bbe28
>         PID: 847
>     COMMAND: "khungtaskd"
>        TASK: ffff94f8038f4000  [THREAD_INFO: ffff94f8038f4000]
>         CPU: 72
>       STATE: TASK_RUNNING (PANIC)
>
>        VMAP_AREA         VM_STRUCT                 ADDRESS RANGE
>       SIZE
>     ffff94eb9102c640  ffff94eb9102b140  ffffb7efce9b8000 -
> ffffb7efce9bd000    20480
>
>
I have one question: If the given physical address falls in the vmalloc
area, it won't print the task context, is that expected? For example:

[1] Before this patch: the "kmem + physical/virtual address" has the same
output asbelow.

crash> kmem ffffb7efce9bbe28
   VMAP_AREA         VM_STRUCT                 ADDRESS RANGE
 SIZE
ffff94eb9102c640  ffff94eb9102b140  ffffb7efce9b8000 - ffffb7efce9bd000
 20480

      PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffdd28220dc000 1883700000                0        0  1 50000000000000

crash> kmem 1883700e28   <----- vtop ffffb7efce9bbe28
   VMAP_AREA         VM_STRUCT                 ADDRESS RANGE
 SIZE
ffff94eb9102c640  ffff94eb9102b140  ffffb7efce9b8000 - ffffb7efce9bd000
 20480

      PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffdd28220dc000 1883700000                0        0  1 50000000000000

[2] After this patch: the "kmem + physical/virtual address" has different
output asbelow.
crash>  kmem ffffb7efce9bbe28
    PID: 847
COMMAND: "khungtaskd"
   TASK: ffff94f8038f4000  [THREAD_INFO: ffff94f8038f4000]
    CPU: 72
  STATE: TASK_RUNNING (PANIC)

   VMAP_AREA         VM_STRUCT                 ADDRESS RANGE
 SIZE
ffff94eb9102c640  ffff94eb9102b140  ffffb7efce9b8000 - ffffb7efce9bd000
 20480

      PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffdd28220dc000 1883700000                0        0  1 50000000000000

crash> kmem 1883700e28  <----- vtop ffffb7efce9bbe28
   VMAP_AREA         VM_STRUCT                 ADDRESS RANGE
 SIZE
ffff94eb9102c640  ffff94eb9102b140  ffffb7efce9b8000 - ffffb7efce9bd000
 20480

      PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffdd28220dc000 1883700000                0        0  1 50000000000000


Thanks.
Lianbo

          PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
>     ffffdd28220dc000 1883700000                0        0  1 50000000000000
>
> Signed-off-by: Tao Liu <ltao at redhat.com>
> ---
>
> v1 -> v2: 1) Remove goto to print task context and vmlist.
>           2) Update commit log to show the change.
>
> ---
>  memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/memory.c b/memory.c
> index 7339f0c..9ab5781 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -13477,6 +13477,10 @@ kmem_search(struct meminfo *mi)
>          *  Check for a valid mapped address.
>          */
>         if ((mi->memtype == KVADDR) && IS_VMALLOC_ADDR(mi->spec_addr)) {
> +               if ((task = stkptr_to_task(vaddr)) && (tc =
> task_to_context(task))) {
> +                       show_context(tc);
> +                       fprintf(fp, "\n");
> +               }
>                 if (kvtop(NULL, mi->spec_addr, &paddr, 0)) {
>                         mi->flags = orig_flags | VMLIST_VERIFY;
>                         dump_vmlist(mi);
> --
> 2.33.1
>
>
>
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