From: Liu Ying Date: Wed, 18 Mar 2026 05:26:05 +0000 (+0800) Subject: drm/bridge: Fix refcount shown via debugfs for encoder_bridges_show() X-Git-Tag: v7.0-rc7~22^2^2~5 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=f078634c184a9b5ccaa056e8b8d6cd32f7bff1b6;p=thirdparty%2Fkernel%2Flinux.git drm/bridge: Fix refcount shown via debugfs for encoder_bridges_show() A typical bridge refcount value is 3 after a bridge chain is formed: - devm_drm_bridge_alloc() initializes the refcount value to be 1. - drm_bridge_add() gets an additional reference hence 2. - drm_bridge_attach() gets the third reference hence 3. This typical refcount value aligns with allbridges_show()'s behaviour. However, since encoder_bridges_show() uses drm_for_each_bridge_in_chain_scoped() to automatically get/put the bridge reference while iterating, a bogus reference is accidentally got when showing the wrong typical refcount value as 4 to users via debugfs. Fix this by caching the refcount value returned from kref_read() while iterating and explicitly decreasing the cached refcount value by 1 before showing it to users. Fixes: bd57048e4576 ("drm/bridge: use drm_for_each_bridge_in_chain_scoped()") Signed-off-by: Liu Ying Reviewed-by: Luca Ceresoli Tested-by: Luca Ceresoli Link: https://patch.msgid.link/20260318-drm-misc-next-2026-03-05-fix-encoder-bridges-refcount-v3-1-147fea581279@nxp.com Signed-off-by: Luca Ceresoli --- diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index d6f11c68bb6a..1987789b258a 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -1569,11 +1569,17 @@ EXPORT_SYMBOL(devm_drm_put_bridge); static void drm_bridge_debugfs_show_bridge(struct drm_printer *p, struct drm_bridge *bridge, unsigned int idx, - bool lingering) + bool lingering, + bool scoped) { + unsigned int refcount = kref_read(&bridge->refcount); + + if (scoped) + refcount--; + drm_printf(p, "bridge[%u]: %ps\n", idx, bridge->funcs); - drm_printf(p, "\trefcount: %u%s\n", kref_read(&bridge->refcount), + drm_printf(p, "\trefcount: %u%s\n", refcount, lingering ? " [lingering]" : ""); drm_printf(p, "\ttype: [%d] %s\n", @@ -1607,10 +1613,10 @@ static int allbridges_show(struct seq_file *m, void *data) mutex_lock(&bridge_lock); list_for_each_entry(bridge, &bridge_list, list) - drm_bridge_debugfs_show_bridge(&p, bridge, idx++, false); + drm_bridge_debugfs_show_bridge(&p, bridge, idx++, false, false); list_for_each_entry(bridge, &bridge_lingering_list, list) - drm_bridge_debugfs_show_bridge(&p, bridge, idx++, true); + drm_bridge_debugfs_show_bridge(&p, bridge, idx++, true, false); mutex_unlock(&bridge_lock); @@ -1625,7 +1631,7 @@ static int encoder_bridges_show(struct seq_file *m, void *data) unsigned int idx = 0; drm_for_each_bridge_in_chain_scoped(encoder, bridge) - drm_bridge_debugfs_show_bridge(&p, bridge, idx++, false); + drm_bridge_debugfs_show_bridge(&p, bridge, idx++, false, true); return 0; }