The patch titled Subject: zram: avoid NULL pointer access in concurrent situation has been added to the -mm tree. Its filename is zram-avoid-null-pointer-access-in-concurrent-situation.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/zram-avoid-null-pointer-access-in-concurrent-situation.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/zram-avoid-null-pointer-access-in-concurrent-situation.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Weijie Yang <weijie.yang@xxxxxxxxxxx> Subject: zram: avoid NULL pointer access in concurrent situation There is a rare NULL pointer bug in mem_used_total_show() and mem_used_max_store() in concurrent situation, like this: zram is not initialized, process A is a mem_used_total reader which runs periodically, 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 <weijie.yang@xxxxxxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/block/zram/zram_drv.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff -puN drivers/block/zram/zram_drv.c~zram-avoid-null-pointer-access-in-concurrent-situation drivers/block/zram/zram_drv.c --- a/drivers/block/zram/zram_drv.c~zram-avoid-null-pointer-access-in-concurrent-situation +++ a/drivers/block/zram/zram_drv.c @@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struc { 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); @@ -173,16 +174,17 @@ static ssize_t mem_used_max_store(struct int err; unsigned long val; struct zram *zram = dev_to_zram(dev); - struct zram_meta *meta = zram->meta; err = kstrtoul(buf, 10, &val); if (err || val != 0) return -EINVAL; down_read(&zram->init_lock); - if (init_done(zram)) + if (init_done(zram)) { + struct zram_meta *meta = zram->meta; atomic_long_set(&zram->stats.max_used_pages, zs_get_total_pages(meta->mem_pool)); + } up_read(&zram->init_lock); return len; _ Patches currently in -mm which might be from weijie.yang@xxxxxxxxxxx are zram-avoid-null-pointer-access-in-concurrent-situation.patch x86-cma-reserve-dma-contiguous-area-after-initmem_init.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html