Re: [PATCH v8 06/14] lockdep: Detect and handle hist_lock ring buffer overwrite

Boqun Feng
2017-08-10T11:59:19Z

[-- Attachment #1: Type: text/plain, Size: 6408 bytes --]

On Mon, Aug 07, 2017 at 04:12:53PM +0900, Byungchul Park wrote:
> The ring buffer can be overwritten by hardirq/softirq/work contexts.
> That cases must be considered on rollback or commit. For example,
>
> |<------ hist_lock ring buffer size ----->|
> ppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
> wrapped > iiiiiiiiiiiiiiiiiiiiiii....................
>
> where 'p' represents an acquisition in process context,
> 'i' represents an acquisition in irq context.
>
> On irq exit, crossrelease tries to rollback idx to original position,
> but it should not because the entry already has been invalid by
> overwriting 'i'. Avoid rollback or commit for entries overwritten.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> include/linux/lockdep.h | 20 +++++++++++++++++++
> include/linux/sched.h | 3 +++
> kernel/locking/lockdep.c | 52 +++++++++++++++++++++++++++++++++++++++++++-----
> 3 files changed, 70 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 0c8a1b8..48c244c 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -284,6 +284,26 @@ struct held_lock {
> */
> struct hist_lock {
> /*
> + * Id for each entry in the ring buffer. This is used to
> + * decide whether the ring buffer was overwritten or not.
> + *
> + * For example,
> + *
> + * |<----------- hist_lock ring buffer size ------->|
> + * pppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiii
> + * wrapped > iiiiiiiiiiiiiiiiiiiiiiiiiii.......................
> + *
> + * where 'p' represents an acquisition in process
> + * context, 'i' represents an acquisition in irq
> + * context.
> + *
> + * In this example, the ring buffer was overwritten by
> + * acquisitions in irq context, that should be detected on
> + * rollback or commit.
> + */
> + unsigned int hist_id;
> +
> + /*
> * Seperate stack_trace data. This will be used at commit step.
> */
> struct stack_trace trace;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5becef5..373466b 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -855,6 +855,9 @@ struct task_struct {
> unsigned int xhlock_idx;
> /* For restoring at history boundaries */
> unsigned int xhlock_idx_hist[CONTEXT_NR];
> + unsigned int hist_id;
> + /* For overwrite check at each context exit */
> + unsigned int hist_id_save[CONTEXT_NR];
> #endif
>
> #ifdef CONFIG_UBSAN
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index afd6e64..5168dac 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4742,6 +4742,17 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
> static atomic_t cross_gen_id; /* Can be wrapped */
>
> /*
> + * Make an entry of the ring buffer invalid.
> + */
> +static inline void invalidate_xhlock(struct hist_lock *xhlock)
> +{
> + /*
> + * Normally, xhlock->hlock.instance must be !NULL.
> + */
> + xhlock->hlock.instance = NULL;
> +}
> +
> +/*
> * Lock history stacks; we have 3 nested lock history stacks:
> *
> * Hard IRQ
> @@ -4773,14 +4784,28 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
> */
> void crossrelease_hist_start(enum context_t c)
> {
> - if (current->xhlocks)
> - current->xhlock_idx_hist[c] = current->xhlock_idx;
> + struct task_struct *cur = current;
> +
> + if (cur->xhlocks) {
> + cur->xhlock_idx_hist[c] = cur->xhlock_idx;
> + cur->hist_id_save[c] = cur->hist_id;
> + }
> }
>
> void crossrelease_hist_end(enum context_t c)
> {
> - if (current->xhlocks)
> - current->xhlock_idx = current->xhlock_idx_hist[c];
> + struct task_struct *cur = current;
> +
> + if (cur->xhlocks) {
> + unsigned int idx = cur->xhlock_idx_hist[c];
> + struct hist_lock *h = &xhlock(idx);
> +
> + cur->xhlock_idx = idx;
> +
> + /* Check if the ring was overwritten. */
> + if (h->hist_id != cur->hist_id_save[c])

Could we use:

if (h->hist_id != idx)

here, and

> + invalidate_xhlock(h);
> + }
> }
>
> static int cross_lock(struct lockdep_map *lock)
> @@ -4826,6 +4851,7 @@ static inline int depend_after(struct held_lock *hlock)
> * Check if the xhlock is valid, which would be false if,
> *
> * 1. Has not used after initializaion yet.
> + * 2. Got invalidated.
> *
> * Remind hist_lock is implemented as a ring buffer.
> */
> @@ -4857,6 +4883,7 @@ static void add_xhlock(struct held_lock *hlock)
>
> /* Initialize hist_lock's members */
> xhlock->hlock = *hlock;
> + xhlock->hist_id = current->hist_id++;

use:

xhlock->hist_id = idx;

and,

>
> xhlock->trace.nr_entries = 0;
> xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
> @@ -4995,6 +5022,7 @@ static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock)
> static void commit_xhlocks(struct cross_lock *xlock)
> {
> unsigned int cur = current->xhlock_idx;
> + unsigned int prev_hist_id = xhlock(cur).hist_id;

use:
unsigned int prev_hist_id = cur;

here.

Then we can get away with the added fields in task_struct at least.

Thought?

Regards,
Boqun

> unsigned int i;
>
> if (!graph_lock())
> @@ -5013,6 +5041,17 @@ static void commit_xhlocks(struct cross_lock *xlock)
> break;
>
> /*
> + * Filter out the cases that the ring buffer was
> + * overwritten and the previous entry has a bigger
> + * hist_id than the following one, which is impossible
> + * otherwise.
> + */
> + if (unlikely(before(xhlock->hist_id, prev_hist_id)))
> + break;
> +
> + prev_hist_id = xhlock->hist_id;
> +
> + /*
> * commit_xhlock() returns 0 with graph_lock already
> * released if fail.
> */
> @@ -5085,9 +5124,12 @@ void lockdep_init_task(struct task_struct *task)
> int i;
>
> task->xhlock_idx = UINT_MAX;
> + task->hist_id = 0;
>
> - for (i = 0; i < CONTEXT_NR; i++)
> + for (i = 0; i < CONTEXT_NR; i++) {
> task->xhlock_idx_hist[i] = UINT_MAX;
> + task->hist_id_save[i] = 0;
> + }
>
> task->xhlocks = kzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR,
> GFP_KERNEL);
> --
> 1.9.1
>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]