[PATCH] x86/resctrl: Fix invalid attempt at removing default resource group

[PATCH] x86/resctrl: Fix invalid attempt at removing default resource group

[Reinette Chatre]

The default resource group ("rdtgroup_default") is associated with the
root of the resctrl filesystem and should never be removed. New resource
groups can be created as subdirectories of the resctrl filesystem and
they can be removed from user space. There exists a safeguard in the
directory removal code (rdtgroup_rmdir()) that ensures that only
subdirectories can be removed by testing that the directory to be
removed has to be a child of the root directory.

A possible deadlock was recently fixed with commit 334b0f4e9b1b
("x86/resctrl: Fix a deadlock due to inaccurate reference"). This fix
involved associating the private data of the "mon_groups" and "mon_data"
directories to the resource group to which they belong instead of NULL
as before. A consequence of this change was that the original safeguard
code preventing removal of "mon_groups" and "mon_data" found in the root
directory failed resulting in attempts to remove the default resource
group that ends in a BUG:

kernel BUG at mm/slub.c:3969!
invalid opcode: 0000 [#1] SMP PTI

Call Trace:
rdtgroup_rmdir+0x16b/0x2c0
kernfs_iop_rmdir+0x5c/0x90
vfs_rmdir+0x7a/0x160
do_rmdir+0x17d/0x1e0
do_syscall_64+0x55/0x1d0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix this by improving the directory removal safeguard to ensure that
subdirectories of the resctrl root directory can only be removed if
they are a child of the resctrl filesystem's root _and_ not associated
with the default resource group.

Fixes: 334b0f4e9b1b ("x86/resctrl: Fix a deadlock due to inaccurate reference")
Cc: stable@vger.kernel.org
Reported-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Tested-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 064e9ef44cd6..9d4e73a9b5a9 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3072,7 +3072,8 @@ static int rdtgroup_rmdir(struct kernfs_node *kn)
 	 * If the rdtgroup is a mon group and parent directory
 	 * is a valid "mon_groups" directory, remove the mon group.
 	 */
-	if (rdtgrp->type == RDTCTRL_GROUP && parent_kn == rdtgroup_default.kn) {
+	if (rdtgrp->type == RDTCTRL_GROUP && parent_kn == rdtgroup_default.kn &&
+	    rdtgrp != &rdtgroup_default) {
 		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
 		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
 			ret = rdtgroup_ctrl_remove(kn, rdtgrp);
-- 
2.21.0

Re: [PATCH] x86/resctrl: Fix invalid attempt at removing default resource group

[Sasha Levin]

Hi

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag
fixing commit: 334b0f4e9b1b ("x86/resctrl: Fix a deadlock due to inaccurate reference").

The bot has tested the following trees: v5.5.9, v5.4.25, v4.19.110, v4.14.173.

v5.5.9: Build OK!
v5.4.25: Build OK!
v4.19.110: Failed to apply! Possible dependencies:
    Unable to calculate

v4.14.173: Failed to apply! Possible dependencies:
    0b9aa6562650 ("x86/intel_rdt: Introduce test to determine if closid is in use")
    2244645ab194 ("x86/intel_rdt: Fix a silent failure when writing zero value schemata")
    472ef09b40c5 ("x86/intel_rdt: Associate mode with each RDT resource group")
    49f7b4efa110 ("x86/intel_rdt: Enable setting of exclusive mode")
    7604df6e16ae ("x86/intel_rdt: Support flexible data to parsing callbacks")
    95f0b77efa57 ("x86/intel_rdt: Initialize new resource group with sane defaults")
    9ab9aa15c309 ("x86/intel_rdt: Ensure requested schemata respects mode")
    9af4c0a6dc1a ("x86/intel_rdt: Making CBM name and type more explicit")
    cfd0f34e4cd5 ("x86/intel_rdt: Add diagnostics when making directories")
    d48d7a57f718 ("x86/intel_rdt: Introduce resource group's mode resctrl file")
    e0bdfe8e36f3 ("x86/intel_rdt: Support creation/removal of pseudo-locked region")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?

-- 
Thanks
Sasha

Re: [PATCH] x86/resctrl: Fix invalid attempt at removing default resource group

[Reinette Chatre]

Hi Thomas and Borislav,

Could you please consider this patch for inclusion as a fix for v5.7?

Thank you

Reinette


On 3/17/2020 9:26 AM, Reinette Chatre wrote:
> The default resource group ("rdtgroup_default") is associated with the
> root of the resctrl filesystem and should never be removed. New resource
> groups can be created as subdirectories of the resctrl filesystem and
> they can be removed from user space. There exists a safeguard in the
> directory removal code (rdtgroup_rmdir()) that ensures that only
> subdirectories can be removed by testing that the directory to be
> removed has to be a child of the root directory.
> 
> A possible deadlock was recently fixed with commit 334b0f4e9b1b
> ("x86/resctrl: Fix a deadlock due to inaccurate reference"). This fix
> involved associating the private data of the "mon_groups" and "mon_data"
> directories to the resource group to which they belong instead of NULL
> as before. A consequence of this change was that the original safeguard
> code preventing removal of "mon_groups" and "mon_data" found in the root
> directory failed resulting in attempts to remove the default resource
> group that ends in a BUG:
> 
> kernel BUG at mm/slub.c:3969!
> invalid opcode: 0000 [#1] SMP PTI
> 
> Call Trace:
> rdtgroup_rmdir+0x16b/0x2c0
> kernfs_iop_rmdir+0x5c/0x90
> vfs_rmdir+0x7a/0x160
> do_rmdir+0x17d/0x1e0
> do_syscall_64+0x55/0x1d0
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Fix this by improving the directory removal safeguard to ensure that
> subdirectories of the resctrl root directory can only be removed if
> they are a child of the resctrl filesystem's root _and_ not associated
> with the default resource group.
> 
> Fixes: 334b0f4e9b1b ("x86/resctrl: Fix a deadlock due to inaccurate reference")
> Cc: stable@vger.kernel.org
> Reported-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Tested-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 064e9ef44cd6..9d4e73a9b5a9 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3072,7 +3072,8 @@ static int rdtgroup_rmdir(struct kernfs_node *kn)
>  	 * If the rdtgroup is a mon group and parent directory
>  	 * is a valid "mon_groups" directory, remove the mon group.
>  	 */
> -	if (rdtgrp->type == RDTCTRL_GROUP && parent_kn == rdtgroup_default.kn) {
> +	if (rdtgrp->type == RDTCTRL_GROUP && parent_kn == rdtgroup_default.kn &&
> +	    rdtgrp != &rdtgroup_default) {
>  		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
>  		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
>  			ret = rdtgroup_ctrl_remove(kn, rdtgrp);
>