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author | Jani Nikula <jani.nikula@intel.com> | 2021-10-01 12:14:44 +0300 |
---|---|---|
committer | Jani Nikula <jani.nikula@intel.com> | 2021-10-13 15:54:46 +0300 |
commit | cd06ab2fd48f2c0243b06344a36056e811d263b8 (patch) | |
tree | 2a45e8267cf5785794eebf6c39ce2043bfb9b8f5 /drivers/gpu/drm/drm_modeset_lock.c | |
parent | 91302d6c1dfd438b53237831f1f78dfbfd8ce934 (diff) | |
download | linux-cd06ab2fd48f2c0243b06344a36056e811d263b8.tar.gz linux-cd06ab2fd48f2c0243b06344a36056e811d263b8.tar.bz2 linux-cd06ab2fd48f2c0243b06344a36056e811d263b8.zip |
drm/locking: add backtrace for locking contended locks without backoff
If drm_modeset_lock() returns -EDEADLK, the caller is supposed to drop
all currently held locks using drm_modeset_backoff(). Failing to do so
will result in warnings and backtraces on the paths trying to lock a
contended lock. Add support for optionally printing the backtrace on the
path that hit the deadlock and didn't gracefully handle the situation.
For example, the patch [1] inadvertently dropped the return value check
and error return on replacing calc_watermark_data() with
intel_compute_global_watermarks(). The backtraces on the subsequent
locking paths hitting WARN_ON(ctx->contended) were unhelpful, but adding
the backtrace to the deadlock path produced this helpful printout:
<7> [98.002465] drm_modeset_lock attempting to lock a contended lock without backoff:
drm_modeset_lock+0x107/0x130
drm_atomic_get_plane_state+0x76/0x150
skl_compute_wm+0x251d/0x2b20 [i915]
intel_atomic_check+0x1942/0x29e0 [i915]
drm_atomic_check_only+0x554/0x910
drm_atomic_nonblocking_commit+0xe/0x50
drm_mode_atomic_ioctl+0x8c2/0xab0
drm_ioctl_kernel+0xac/0x140
Add new CONFIG_DRM_DEBUG_MODESET_LOCK to enable modeset lock debugging
with stack depot and trace.
[1] https://lore.kernel.org/r/20210924114741.15940-4-jani.nikula@intel.com
v2:
- default y if DEBUG_WW_MUTEX_SLOWPATH (Daniel)
- depends on DEBUG_KERNEL
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Dave Airlie <airlied@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211001091444.8177-1-jani.nikula@intel.com
Diffstat (limited to 'drivers/gpu/drm/drm_modeset_lock.c')
-rw-r--r-- | drivers/gpu/drm/drm_modeset_lock.c | 49 |
1 files changed, 47 insertions, 2 deletions
diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c index fcfe1a03c4a1..62f6fe482d25 100644 --- a/drivers/gpu/drm/drm_modeset_lock.c +++ b/drivers/gpu/drm/drm_modeset_lock.c @@ -25,6 +25,7 @@ #include <drm/drm_crtc.h> #include <drm/drm_device.h> #include <drm/drm_modeset_lock.h> +#include <drm/drm_print.h> /** * DOC: kms locking @@ -77,6 +78,45 @@ static DEFINE_WW_CLASS(crtc_ww_class); +#if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK) +static noinline depot_stack_handle_t __stack_depot_save(void) +{ + unsigned long entries[8]; + unsigned int n; + + n = stack_trace_save(entries, ARRAY_SIZE(entries), 1); + + return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN); +} + +static void __stack_depot_print(depot_stack_handle_t stack_depot) +{ + struct drm_printer p = drm_debug_printer("drm_modeset_lock"); + unsigned long *entries; + unsigned int nr_entries; + char *buf; + + buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN); + if (!buf) + return; + + nr_entries = stack_depot_fetch(stack_depot, &entries); + stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2); + + drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf); + + kfree(buf); +} +#else /* CONFIG_DRM_DEBUG_MODESET_LOCK */ +static depot_stack_handle_t __stack_depot_save(void) +{ + return 0; +} +static void __stack_depot_print(depot_stack_handle_t stack_depot) +{ +} +#endif /* CONFIG_DRM_DEBUG_MODESET_LOCK */ + /** * drm_modeset_lock_all - take all modeset locks * @dev: DRM device @@ -225,7 +265,9 @@ EXPORT_SYMBOL(drm_modeset_acquire_fini); */ void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) { - WARN_ON(ctx->contended); + if (WARN_ON(ctx->contended)) + __stack_depot_print(ctx->stack_depot); + while (!list_empty(&ctx->locked)) { struct drm_modeset_lock *lock; @@ -243,7 +285,8 @@ static inline int modeset_lock(struct drm_modeset_lock *lock, { int ret; - WARN_ON(ctx->contended); + if (WARN_ON(ctx->contended)) + __stack_depot_print(ctx->stack_depot); if (ctx->trylock_only) { lockdep_assert_held(&ctx->ww_ctx); @@ -274,6 +317,7 @@ static inline int modeset_lock(struct drm_modeset_lock *lock, ret = 0; } else if (ret == -EDEADLK) { ctx->contended = lock; + ctx->stack_depot = __stack_depot_save(); } return ret; @@ -296,6 +340,7 @@ int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) struct drm_modeset_lock *contended = ctx->contended; ctx->contended = NULL; + ctx->stack_depot = 0; if (WARN_ON(!contended)) return 0; |