From 6c881ca0b3040f3e724eae513117ba4ddef86057 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 15 Jun 2021 11:57:26 +0100 Subject: afs: Fix tracepoint string placement with built-in AFS To quote Alexey[1]: 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. Steps to reproduce: CONFIG_AFS=y CONFIG_TRACING=y # cat /sys/kernel/tracing/printk_formats Fix this by the following means: (1) Add enum->string translation tables in the event header with the AFS and YFS cache/callback manager operations listed by RPC operation ID. (2) Modify the afs_cb_call tracepoint to print the string from the translation table rather than using the string at the afs_call name pointer. (3) Switch translation table depending on the service we're being accessed as (AFS or YFS) in the tracepoint print clause. Will this cause problems to userspace utilities? Note that the symbolic representation of the YFS service ID isn't available to this header, so I've put it in as a number. I'm not sure if this is the best way to do this. (4) Remove the name wrangling (CM_NAME) macro and put the names directly into the afs_call_type structs in cmservice.c. Fixes: 8e8d7f13b6d5a9 ("afs: Add some tracepoints") Reported-by: Alexey Dobriyan (SK hynix) Signed-off-by: David Howells Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Marc Dionne cc: Andrew Morton cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/YLAXfvZ+rObEOdc%2F@localhost.localdomain/ [1] Link: https://lore.kernel.org/r/643721.1623754699@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/162430903582.2896199.6098150063997983353.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/162609463957.3133237.15916579353149746363.stgit@warthog.procyon.org.uk/ # v1 (repost) Link: https://lore.kernel.org/r/162610726860.3408253.445207609466288531.stgit@warthog.procyon.org.uk/ # v2 --- fs/afs/cmservice.c | 25 +++++++------------------ 1 file changed, 7 insertions(+), 18 deletions(-) (limited to 'fs/afs') diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c index d3c6bb22c5f4..a3f5de28be79 100644 --- a/fs/afs/cmservice.c +++ b/fs/afs/cmservice.c @@ -29,16 +29,11 @@ static void SRXAFSCB_TellMeAboutYourself(struct work_struct *); static int afs_deliver_yfs_cb_callback(struct afs_call *); -#define CM_NAME(name) \ - char afs_SRXCB##name##_name[] __tracepoint_string = \ - "CB." #name - /* * CB.CallBack operation type */ -static CM_NAME(CallBack); static const struct afs_call_type afs_SRXCBCallBack = { - .name = afs_SRXCBCallBack_name, + .name = "CB.CallBack", .deliver = afs_deliver_cb_callback, .destructor = afs_cm_destructor, .work = SRXAFSCB_CallBack, @@ -47,9 +42,8 @@ static const struct afs_call_type afs_SRXCBCallBack = { /* * CB.InitCallBackState operation type */ -static CM_NAME(InitCallBackState); static const struct afs_call_type afs_SRXCBInitCallBackState = { - .name = afs_SRXCBInitCallBackState_name, + .name = "CB.InitCallBackState", .deliver = afs_deliver_cb_init_call_back_state, .destructor = afs_cm_destructor, .work = SRXAFSCB_InitCallBackState, @@ -58,9 +52,8 @@ static const struct afs_call_type afs_SRXCBInitCallBackState = { /* * CB.InitCallBackState3 operation type */ -static CM_NAME(InitCallBackState3); static const struct afs_call_type afs_SRXCBInitCallBackState3 = { - .name = afs_SRXCBInitCallBackState3_name, + .name = "CB.InitCallBackState3", .deliver = afs_deliver_cb_init_call_back_state3, .destructor = afs_cm_destructor, .work = SRXAFSCB_InitCallBackState, @@ -69,9 +62,8 @@ static const struct afs_call_type afs_SRXCBInitCallBackState3 = { /* * CB.Probe operation type */ -static CM_NAME(Probe); static const struct afs_call_type afs_SRXCBProbe = { - .name = afs_SRXCBProbe_name, + .name = "CB.Probe", .deliver = afs_deliver_cb_probe, .destructor = afs_cm_destructor, .work = SRXAFSCB_Probe, @@ -80,9 +72,8 @@ static const struct afs_call_type afs_SRXCBProbe = { /* * CB.ProbeUuid operation type */ -static CM_NAME(ProbeUuid); static const struct afs_call_type afs_SRXCBProbeUuid = { - .name = afs_SRXCBProbeUuid_name, + .name = "CB.ProbeUuid", .deliver = afs_deliver_cb_probe_uuid, .destructor = afs_cm_destructor, .work = SRXAFSCB_ProbeUuid, @@ -91,9 +82,8 @@ static const struct afs_call_type afs_SRXCBProbeUuid = { /* * CB.TellMeAboutYourself operation type */ -static CM_NAME(TellMeAboutYourself); static const struct afs_call_type afs_SRXCBTellMeAboutYourself = { - .name = afs_SRXCBTellMeAboutYourself_name, + .name = "CB.TellMeAboutYourself", .deliver = afs_deliver_cb_tell_me_about_yourself, .destructor = afs_cm_destructor, .work = SRXAFSCB_TellMeAboutYourself, @@ -102,9 +92,8 @@ static const struct afs_call_type afs_SRXCBTellMeAboutYourself = { /* * YFS CB.CallBack operation type */ -static CM_NAME(YFS_CallBack); static const struct afs_call_type afs_SRXYFSCB_CallBack = { - .name = afs_SRXCBYFS_CallBack_name, + .name = "YFSCB.CallBack", .deliver = afs_deliver_yfs_cb_callback, .destructor = afs_cm_destructor, .work = SRXAFSCB_CallBack, -- cgit v1.2.3