[PATCHv3] fs/proc: allow reporting eip/esp for all coredumping threads

[PATCHv3] fs/proc: allow reporting eip/esp for all coredumping threads

[John Ogness]

Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
/proc/PID/stat") stopped reporting eip/esp and commit fd7d56270b52
("fs/proc: Report eip/esp in /prod/PID/stat for coredumping")
reintroduced the feature to fix a regression with userspace core dump
handlers (such as minicoredumper).

Because PF_DUMPCORE is only set for the primary thread, this didn't fix
the original problem for secondary threads. Allow reporting the eip/esp
for all threads by checking for PF_EXITING as well. This is set for all
the other threads when they are killed. coredump_wait() waits for all
the tasks to become inactive before proceeding to invoke a core dumper.

Fixes: fd7d56270b526ca3 ("fs/proc: Report eip/esp in /prod/PID/stat for coredumping")
Reported-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 This is a rework of Jan's v1 patch that allows accessing eip/esp of all
 the threads without risk of the task still executing on a CPU.

 The code chagnes are the same as v2. With v3 I included a "Fixes" tag,
 fixed a typo in the commit message, and Cc'd stable.

 fs/proc/array.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 2edbb657f859..55180501b915 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -462,7 +462,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		 * a program is not able to use ptrace(2) in that case. It is
 		 * safe because the task has stopped executing permanently.
 		 */
-		if (permitted && (task->flags & PF_DUMPCORE)) {
+		if (permitted && (task->flags & (PF_EXITING|PF_DUMPCORE))) {
 			if (try_get_task_stack(task)) {
 				eip = KSTK_EIP(task);
 				esp = KSTK_ESP(task);
-- 
2.11.0

Re: [PATCHv3] fs/proc: allow reporting eip/esp for all coredumping threads

[Andrew Morton]

(ooh, Greg, let me do it!)

On Thu, 30 May 2019 02:58:59 +0200 John Ogness <john.ogness@linutronix.de> wrote:

> Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
> /proc/PID/stat") stopped reporting eip/esp and commit fd7d56270b52
> ("fs/proc: Report eip/esp in /prod/PID/stat for coredumping")
> reintroduced the feature to fix a regression with userspace core dump
> handlers (such as minicoredumper).
> 
> Because PF_DUMPCORE is only set for the primary thread, this didn't fix
> the original problem for secondary threads. Allow reporting the eip/esp
> for all threads by checking for PF_EXITING as well. This is set for all
> the other threads when they are killed. coredump_wait() waits for all
> the tasks to become inactive before proceeding to invoke a core dumper.
> 
> Fixes: fd7d56270b526ca3 ("fs/proc: Report eip/esp in /prod/PID/stat for coredumping")
> Reported-by: Jan Luebbe <jlu@pengutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  This is a rework of Jan's v1 patch that allows accessing eip/esp of all
>  the threads without risk of the task still executing on a CPU.
> 
>  The code chagnes are the same as v2. With v3 I included a "Fixes" tag,
>  fixed a typo in the commit message, and Cc'd stable.

No, the way to Cc stable is to add

Cc: <stable@vger.kernel.org> to the changelog metadata.

I've made these changes to my copy of this patch, thanks.

Re: [PATCHv3] fs/proc: allow reporting eip/esp for all coredumping threads

[Jan Lübbe]

On Thu, 2019-05-30 at 02:58 +0200, John Ogness wrote:
> Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
> /proc/PID/stat") stopped reporting eip/esp and commit fd7d56270b52
> ("fs/proc: Report eip/esp in /prod/PID/stat for coredumping")
> reintroduced the feature to fix a regression with userspace core dump
> handlers (such as minicoredumper).
> 
> Because PF_DUMPCORE is only set for the primary thread, this didn't fix
> the original problem for secondary threads. Allow reporting the eip/esp
> for all threads by checking for PF_EXITING as well. This is set for all
> the other threads when they are killed. coredump_wait() waits for all
> the tasks to become inactive before proceeding to invoke a core dumper.
> 
> Fixes: fd7d56270b526ca3 ("fs/proc: Report eip/esp in /prod/PID/stat for coredumping")
> Reported-by: Jan Luebbe <jlu@pengutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Tested-by: Jan Luebbe <jlu@pengutronix.de>

I've tested your patch and can confirm that eip/esp is accessible for
all threads again.

Thanks,
Jan
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