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preview_data: guard the pipe-nodes walk in dt_preview_data_is_fresh with busy_mutex #22119

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Merged
TurboGit merged 1 commit into from
Sep 2, 2026
Merged

preview_data: guard the pipe-nodes walk in dt_preview_data_is_fresh with busy_mutex #22119

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21 changes: 18 additions & 3 deletions src/develop/preview_data.c
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Original file line number Diff line number Diff line change
Expand Up @@ -179,13 +179,27 @@ gboolean dt_preview_data_is_fresh(dt_preview_data_t *pd)

if(fresh)
{
const dt_develop_t *const dev = module->dev;
if(!dev || !dev->preview_pipe)
dt_dev_pixelpipe_t *const pipe = module->dev ? module->dev->preview_pipe : NULL;
if(!pipe)
fresh = FALSE;
// pipe->nodes (and the pieces it points to) are only safe to walk while
// holding busy_mutex: a concurrent history change can rebuild the whole
// list -- dt_dev_pixelpipe_cleanup_nodes() frees every piece -- while this
// runs on the GUI thread, outside that protection, causing a
// dangling-pointer segfault in the hash walk below. Must be a trylock,
// not a blocking lock: a module's process() runs under busy_mutex for
// the whole pipe run (dt_dev_pixelpipe_process) and can itself call
// dt_preview_data_store(), which takes this same module's gui_lock
// (already held above) -- the opposite order -- so a blocking lock here
// would AB-BA deadlock against it. A pipe that's currently busy can't
// have fresh data for us anyway, so treating "busy" as "not fresh"
// costs nothing.
else if(dt_pthread_mutex_trylock(&pipe->busy_mutex))
fresh = FALSE;
else
{
dt_dev_pixelpipe_iop_t *piece = NULL;
for(GList *iter = dev->preview_pipe->nodes; iter; iter = g_list_next(iter))
for(GList *iter = pipe->nodes; iter; iter = g_list_next(iter))
{
dt_dev_pixelpipe_iop_t *const p = (dt_dev_pixelpipe_iop_t *)iter->data;
if(p->module == module)
Expand All @@ -201,6 +215,7 @@ gboolean dt_preview_data_is_fresh(dt_preview_data_t *pd)
const dt_hash_t cur_hash = dt_dev_pixelpipe_piece_hash(piece, &piece->processed_roi_out, TRUE);
fresh = (cur_hash == stored_hash);
}
dt_pthread_mutex_unlock(&pipe->busy_mutex);
}
}

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