4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai <tiwai@xxxxxxx> commit c520ff3d03f0b5db7146d9beed6373ad5d2a5e0e upstream. When snd_seq_pool_done() is called, it marks the closing flag to refuse the further cell insertions. But snd_seq_pool_done() itself doesn't clear the cells but just waits until all cells are cleared by the caller side. That is, it's racy, and this leads to the endless stall as syzkaller spotted. This patch addresses the racy by splitting the setup of pool->closing flag out of snd_seq_pool_done(), and calling it properly before snd_seq_pool_done(). BugLink: http://lkml.kernel.org/r/CACT4Y+aqqy8bZA1fFieifNxR2fAfFQQABcBHj801+u5ePV0URw@xxxxxxxxxxxxxx Reported-and-tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- sound/core/seq/seq_clientmgr.c | 1 + sound/core/seq/seq_fifo.c | 3 +++ sound/core/seq/seq_memory.c | 17 +++++++++++++---- sound/core/seq/seq_memory.h | 1 + 4 files changed, 18 insertions(+), 4 deletions(-) --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -1921,6 +1921,7 @@ static int snd_seq_ioctl_set_client_pool info.output_pool != client->pool->size)) { if (snd_seq_write_pool_allocated(client)) { /* remove all existing cells */ + snd_seq_pool_mark_closing(client->pool); snd_seq_queue_client_leave_cells(client->number); snd_seq_pool_done(client->pool); } --- a/sound/core/seq/seq_fifo.c +++ b/sound/core/seq/seq_fifo.c @@ -70,6 +70,9 @@ void snd_seq_fifo_delete(struct snd_seq_ return; *fifo = NULL; + if (f->pool) + snd_seq_pool_mark_closing(f->pool); + snd_seq_fifo_clear(f); /* wake up clients if any */ --- a/sound/core/seq/seq_memory.c +++ b/sound/core/seq/seq_memory.c @@ -414,6 +414,18 @@ int snd_seq_pool_init(struct snd_seq_poo return 0; } +/* refuse the further insertion to the pool */ +void snd_seq_pool_mark_closing(struct snd_seq_pool *pool) +{ + unsigned long flags; + + if (snd_BUG_ON(!pool)) + return; + spin_lock_irqsave(&pool->lock, flags); + pool->closing = 1; + spin_unlock_irqrestore(&pool->lock, flags); +} + /* remove events */ int snd_seq_pool_done(struct snd_seq_pool *pool) { @@ -424,10 +436,6 @@ int snd_seq_pool_done(struct snd_seq_poo return -EINVAL; /* wait for closing all threads */ - spin_lock_irqsave(&pool->lock, flags); - pool->closing = 1; - spin_unlock_irqrestore(&pool->lock, flags); - if (waitqueue_active(&pool->output_sleep)) wake_up(&pool->output_sleep); @@ -484,6 +492,7 @@ int snd_seq_pool_delete(struct snd_seq_p *ppool = NULL; if (pool == NULL) return 0; + snd_seq_pool_mark_closing(pool); snd_seq_pool_done(pool); kfree(pool); return 0; --- a/sound/core/seq/seq_memory.h +++ b/sound/core/seq/seq_memory.h @@ -84,6 +84,7 @@ static inline int snd_seq_total_cells(st int snd_seq_pool_init(struct snd_seq_pool *pool); /* done pool - free events */ +void snd_seq_pool_mark_closing(struct snd_seq_pool *pool); int snd_seq_pool_done(struct snd_seq_pool *pool); /* create pool */