On (10/25/14 17:26), Weijie Yang wrote: > Date: Sat, 25 Oct 2014 17:26:31 +0800 > From: Weijie Yang <[email protected]> > To: 'Minchan Kim' <[email protected]> > Cc: 'Andrew Morton' <[email protected]>, 'Dan Streetman' > <[email protected]>, 'Sergey Senozhatsky' <[email protected]>, > 'Nitin Gupta' <[email protected]>, 'Linux-MM' <[email protected]>, > 'linux-kernel' <[email protected]>, 'Weijie Yang' > <[email protected]> > Subject: [PATCH 2/2] zram: avoid NULL pointer access when reading > mem_used_total > X-Mailer: Microsoft Office Outlook 12.0 > > There is a rare NULL pointer bug in mem_used_total_show() in concurrent > situation, like this: > zram is not initialized, process A is a mem_used_total reader which runs > periodicity, while process B try to init zram. > > process A process B > access meta, get a NULL value > init zram, done > init_done() is true > access meta->mem_pool, get a NULL pointer BUG > > This patch fixes this issue. > > Signed-off-by: Weijie Yang <[email protected]>
Acked-by: Sergey Senozhatsky <[email protected]> -ss > --- > drivers/block/zram/zram_drv.c | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 64dd79a..2ffd7d8 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struct device *dev, > { > u64 val = 0; > struct zram *zram = dev_to_zram(dev); > - struct zram_meta *meta = zram->meta; > > down_read(&zram->init_lock); > - if (init_done(zram)) > + if (init_done(zram)) { > + struct zram_meta *meta = zram->meta; > val = zs_get_total_pages(meta->mem_pool); > + } > up_read(&zram->init_lock); > > return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT); > -- > 1.7.0.4 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
