The patch titled Subject: afs: fix tracepoint string placement with built-in AFS has been added to the -mm tree. Its filename is afs-fix-tracepoint-string-placement-with-built-in-afs.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/afs-fix-tracepoint-string-placemen... and later at https://ozlabs.org/~akpm/mmotm/broken-out/afs-fix-tracepoint-string-placemen...

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated there every 3-4 working days

------------------------------------------------------ From: Alexey Dobriyan adobriyan@gmail.com Subject: afs: fix tracepoint string placement with built-in AFS

I was adding custom tracepoint to the kernel, grabbed full F34 kernel .config, disabled modules and booted whole shebang as VM kernel.

Then did

perf record -a -e ...

It crashed:

general protection fault, probably for non-canonical address 0x435f5346592e4243: 0000 [#1] SMP PTI CPU: 1 PID: 842 Comm: cat Not tainted 5.12.6+ #26 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014 RIP: 0010:t_show+0x22/0xd0

Then reproducer was narrowed to

# cat /sys/kernel/tracing/printk_formats

Original F34 kernel with modules didn't crash.

So I started to disable options and after disabling AFS everything started working again.

The root cause is that AFS was placing char arrays content into a section full of _pointers_ to strings with predictable consequences.

Non canonical address 435f5346592e4243 is "CB.YFS_" which came from CM_NAME macro.

The fix is to create char array and pointer to it separatedly.

Steps to reproduce:

CONFIG_AFS=y CONFIG_TRACING=y

# cat /sys/kernel/tracing/printk_formats

Link: https://lkml.kernel.org/r/YLAXfvZ+rObEOdc/@localhost.localdomain Fixes: 8e8d7f13b6d5a9 ("afs: Add some tracepoints") Signed-off-by: Alexey Dobriyan (SK hynix) adobriyan@gmail.com Cc: Andi Kleen andi@firstfloor.org Cc: David Howells dhowells@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/afs/cmservice.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/afs/cmservice.c~afs-fix-tracepoint-string-placement-with-built-in-afs +++ a/fs/afs/cmservice.c @@ -30,8 +30,9 @@ static void SRXAFSCB_TellMeAboutYourself static int afs_deliver_yfs_cb_callback(struct afs_call *);

#define CM_NAME(name) \ - char afs_SRXCB##name##_name[] __tracepoint_string = \ - "CB." #name + const char afs_SRXCB##name##_name[] = "CB." #name; \ + static const char *_afs_SRXCB##name##_name __tracepoint_string =\ + afs_SRXCB##name##_name

/* * CB.CallBack operation type _

Patches currently in -mm which might be from adobriyan@gmail.com are

afs-fix-tracepoint-string-placement-with-built-in-afs.patch lib-memscan-fixlet.patch lib-uninline-simple_strtoull.patch exec-remove-checks-in-__register_bimfmt.patch