Hi Vinod, > From: Vinod Koul [mailto:vinod.koul@xxxxxxxxx] > Sent: Monday, November 16, 2015 12:47 PM > > On Thu, Nov 12, 2015 at 01:37:40PM +0900, Yoshihiro Shimoda wrote: > > This patch fixes an issue that list_for_each_entry() in > > usb_dmac_chan_terminate_all() is possible to cause endless loop because > > this will move own desc to the desc_freed. So, this driver should use > > list_for_each_entry_safe() instead of list_for_each_entry(). > > Sorry this is not clear to my why this owuld have endless loop, can you > explain more This issue will happens if &uchan->desc_got has one or more lists. (In other words, there was a potential problem from the first commit of this driver...) This is because that this driver use "desc" for list_move_tail() as the first argument, and the list_move_tail() calls __list_del_entry(). So, the desc may be wrong list_head for list_next_entry(). static int usb_dmac_chan_terminate_all(struct dma_chan *chan) { <snip> list_splice_init(&uchan->desc_got, &list); list_for_each_entry(desc, &list, node) list_move_tail(&desc->node, &uchan->desc_freed); < in include/linux/list.h > static inline void list_move_tail(struct list_head *list, struct list_head *head) { __list_del_entry(list); list_add_tail(list, head); } If I enabled CONFIG_DEBUG_LIST, the following WARNING happened: ------------[ cut here ]------------ WARNING: CPU: 2 PID: 2477 at lib/list_debug.c:33 __list_add+0x64/0xb0() list_add corruption. prev->next should be next (edca6098), but was ee936e00. (prev=ee936ec0). Modules linked in: g_mass_storage(-) usb_f_mass_storage libcomposite CPU: 2 PID: 2477 Comm: file-storage Not tainted 4.3.0-rc1-00002-g4d15d22 #27 Hardware name: Generic R8A7790 (Flattened Device Tree) Backtrace: [<c00137a0>] (dump_backtrace) from [<c0013998>] (show_stack+0x18/0x1c) r7:c05d2664 r6:ee92e140 r5:00000009 r4:00000000 [<c0013980>] (show_stack) from [<c01be7d0>] (dump_stack+0x78/0x94) [<c01be758>] (dump_stack) from [<c0025224>] (warn_slowpath_common+0x8c/0xb8) r5:00000009 r4:ee22bd90 [<c0025198>] (warn_slowpath_common) from [<c0025288>] (warn_slowpath_fmt+0x38/0x40) r9:edca6098 r8:a0000093 r7:edca605c r6:edca6098 r5:edca6098 r4:ee936ec0 [<c0025254>] (warn_slowpath_fmt) from [<c01d49b8>] (__list_add+0x64/0xb0) r3:edca6098 r2:c05d2675 [<c01d4954>] (__list_add) from [<c0202e5c>] (usb_dmac_chan_terminate_all+0x14c/0x17c) r6:ee22bde0 r5:edca6058 r4:edca6010 [<c0202d10>] (usb_dmac_chan_terminate_all) from [<c02e84b0>] (usbhs_pkt_pop+0xa0/0xf4) < snip > Best regards, Yoshihiro Shimoda > > > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> > > --- > > drivers/dma/sh/usb-dmac.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/dma/sh/usb-dmac.c b/drivers/dma/sh/usb-dmac.c > > index ebd8a5f..16fb330 100644 > > --- a/drivers/dma/sh/usb-dmac.c > > +++ b/drivers/dma/sh/usb-dmac.c > > @@ -448,7 +448,7 @@ usb_dmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl, > > static int usb_dmac_chan_terminate_all(struct dma_chan *chan) > > { > > struct usb_dmac_chan *uchan = to_usb_dmac_chan(chan); > > - struct usb_dmac_desc *desc; > > + struct usb_dmac_desc *desc, *_desc; > > unsigned long flags; > > LIST_HEAD(head); > > LIST_HEAD(list); > > @@ -459,7 +459,7 @@ static int usb_dmac_chan_terminate_all(struct dma_chan *chan) > > if (uchan->desc) > > uchan->desc = NULL; > > list_splice_init(&uchan->desc_got, &list); > > - list_for_each_entry(desc, &list, node) > > + list_for_each_entry_safe(desc, _desc, &list, node) > > list_move_tail(&desc->node, &uchan->desc_freed); > > spin_unlock_irqrestore(&uchan->vc.lock, flags); > > vchan_dma_desc_free_list(&uchan->vc, &head); > > -- > > 1.9.1 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe dmaengine" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
