On Tue, Aug 06, 2013 at 01:26:34AM +0900, Minchan Kim wrote: > On Mon, Aug 05, 2013 at 04:18:34PM +0900, Minchan Kim wrote: > > I was preparing to promote zram and it was almost done. > > Before sending patch, I tried to test and eyebrows went up. > > > > [1] introduced down_write in zram_slot_free_notify to prevent race > > between zram_slot_free_notify and zram_bvec_[read|write]. The race > > could happen if somebody who has right permission to open swap device > > is reading swap device while it is used by swap in parallel. > > > > However, zram_slot_free_notify is called with holding spin_lock of > > swap layer so we shouldn't avoid holing mutex. Otherwise, lockdep > > warns it. > > > > I guess, best solution is to redesign zram lock scheme totally but > > we are on the verge of promoting so it's not desirable to change a lot > > critical code and such big change isn't good shape for backporting to > > stable trees so I think the simple patch is best at the moment. > > > > [1] [57ab0485, zram: use zram->lock to protect zram_free_page() > > in swap free notify path] > > > > Cc: Jiang Liu <jiang.liu@xxxxxxxxxx> > > Cc: Nitin Gupta <ngupta@xxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > --- > > drivers/staging/zram/zram_drv.c | 15 ++++++++++++++- > > 1 file changed, 14 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c > > index 7ebf91d..7b574c4 100644 > > --- a/drivers/staging/zram/zram_drv.c > > +++ b/drivers/staging/zram/zram_drv.c > > @@ -440,6 +440,13 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, > > goto out; > > } > > > > + /* > > + * zram_slot_free_notify could miss free so that let's > > + * double check. > > + */ > > + if (unlikely(meta->table[index].handle)) > > + zram_free_page(zram, index); > > + > > ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen, > > meta->compress_workmem); > > > > @@ -727,7 +734,13 @@ static void zram_slot_free_notify(struct block_device *bdev, > > struct zram *zram; > > > > zram = bdev->bd_disk->private_data; > > - down_write(&zram->lock); > > + /* > > + * The function is called in atomic context so down_write should > > + * be prohibited. If we couldn't hold a mutex, the free could be > > + * handled by zram_bvec_write later when same index is overwritten. > > + */ > > + if (!down_write_trylock(&zram->lock)) > > + return; > > zram_free_page(zram, index); > > up_write(&zram->lock); > > atomic64_inc(&zram->stats.notify_free); > > -- > > 1.7.9.5 > > > > How about this version? I'm guessing you tested it out? If so, please resend in a format that I can apply it in. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html