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    Subject[PATCH V2] x86/resctrl: Fix rdt_find_domain() return value and checks
    Date
    rdt_find_domain() returns an ERR_PTR() that is generated from a provided
    domain id when the value is negative.

    Care needs to be taken when creating an ERR_PTR() from this value because
    a subsequent check using IS_ERR() expects the error to be within the
    MAX_ERRNO range. By using an invalid domain id as an ERR_PTR() does
    work at this time since this is currently always -1. Using this
    undocumented assumption is fragile since future users of
    rdt_find_domain() may not be aware of thus assumption.

    Two related issues are addressed:
    - Ensure that rdt_find_domain() always returns a valid error value by
    forcing the error to be -ENODEV when a negative domain id is provided.
    - In a few instances the return value of rdt_find_domain() is just checked
    for NULL - fix these to include a check of ERR_PTR.

    Fixes: d89b7379015f ("x86/intel_rdt/cqm: Add mon_data")
    Fixes: 521348b011d6 ("x86/intel_rdt: Introduce utility to obtain CDP peer")
    Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
    ---
    V2:
    - Force error value to be -ENODEV when negative domain id provided
    - Rewrite commit message to describe why error value needs to be forced in
    addition to the original fix

    arch/x86/kernel/cpu/resctrl/core.c | 2 +-
    arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 2 +-
    arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 +-
    3 files changed, 3 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
    index 2ec252be4ed9..c3a9dc63edf2 100644
    --- a/arch/x86/kernel/cpu/resctrl/core.c
    +++ b/arch/x86/kernel/cpu/resctrl/core.c
    @@ -454,7 +454,7 @@ struct rdt_domain *rdt_find_domain(struct rdt_resource *r, int id,
    struct list_head *l;

    if (id < 0)
    - return ERR_PTR(id);
    + return ERR_PTR(-ENODEV);

    list_for_each(l, &r->domains) {
    d = list_entry(l, struct rdt_domain, list);
    diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
    index ba11f54f5ab8..3b943ace786c 100644
    --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
    +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
    @@ -534,7 +534,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)

    r = &rdt_resources_all[resid];
    d = rdt_find_domain(r, domid, NULL);
    - if (!d) {
    + if (IS_ERR_OR_NULL(d)) {
    ret = -ENOENT;
    goto out;
    }
    diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
    index 017505017bdb..8388adf241b2 100644
    --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
    +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
    @@ -1029,7 +1029,7 @@ static int rdt_cdp_peer_get(struct rdt_resource *r, struct rdt_domain *d,
    * peer RDT CDP resource. Hence the WARN.
    */
    _d_cdp = rdt_find_domain(_r_cdp, d->id, NULL);
    - if (WARN_ON(!_d_cdp)) {
    + if (WARN_ON(IS_ERR_OR_NULL(_d_cdp))) {
    _r_cdp = NULL;
    ret = -EINVAL;
    }
    --
    2.17.0
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