Hello Sergey 2015-01-23 22:38 GMT+08:00 Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>: > On (01/23/15 14:58), Minchan Kim wrote: >> The zram->stat handling should be procted by init_lock. >> Otherwise, user could see stale value from the stat. >> >> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> >> --- >> >> I don't think it's stable material. The race is rare in real practice >> and this stale stat value read is not a critical. >> >> drivers/block/zram/zram_drv.c | 37 ++++++++++++++++++++++++++++--------- >> 1 file changed, 28 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c >> index 0299d82275e7..53f176f590b0 100644 >> --- a/drivers/block/zram/zram_drv.c >> +++ b/drivers/block/zram/zram_drv.c >> @@ -48,8 +48,13 @@ static ssize_t name##_show(struct device *d, \ >> struct device_attribute *attr, char *b) \ >> { \ > > a side note: I wasn't Cc'd in that patchset and found out it only when it's > been merged. I'm not sure I understand, why it has been renamed from specific > zram_X_show to X_show. what gives? I changed from zram_attr_##name##_show to name##_show in commit: fcf1bce zram: use DEVICE_ATTR_[RW|RO|WO] to define zram sys device attribute I just want to keep the name consistent with others, like disksize_show(), initstate_show(). Thanks. > > > can't help, catches my eye every time, that rename has broken the original > formatting: > > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 9250b3f..c567af5 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -44,7 +44,7 @@ static const char *default_compressor = "lzo"; > static unsigned int num_devices = 1; > > #define ZRAM_ATTR_RO(name) \ > -static ssize_t name##_show(struct device *d, \ > +static ssize_t name##_show(struct device *d, \ > struct device_attribute *attr, char *b) \ > { \ > struct zram *zram = dev_to_zram(d); \ > > > > I don't have any objections. but do we really want to wrap atomic ops in > semaphore? it is really such serious race? > > > -ss > >> struct zram *zram = dev_to_zram(d); \ >> - return scnprintf(b, PAGE_SIZE, "%llu\n", \ >> - (u64)atomic64_read(&zram->stats.name)); \ >> + u64 val = 0; \ >> + \ >> + down_read(&zram->init_lock); \ >> + if (init_done(zram)) \ >> + val = atomic64_read(&zram->stats.name); \ >> + up_read(&zram->init_lock); \ >> + return scnprintf(b, PAGE_SIZE, "%llu\n", val); \ >> } \ >> static DEVICE_ATTR_RO(name); >> >> @@ -67,8 +72,14 @@ static ssize_t disksize_show(struct device *dev, >> struct device_attribute *attr, char *buf) >> { >> struct zram *zram = dev_to_zram(dev); >> + u64 val = 0; >> + >> + down_read(&zram->init_lock); >> + if (init_done(zram)) >> + val = zram->disksize; >> + up_read(&zram->init_lock); >> >> - return scnprintf(buf, PAGE_SIZE, "%llu\n", zram->disksize); >> + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); >> } >> >> static ssize_t initstate_show(struct device *dev, >> @@ -88,9 +99,14 @@ static ssize_t orig_data_size_show(struct device *dev, >> struct device_attribute *attr, char *buf) >> { >> struct zram *zram = dev_to_zram(dev); >> + u64 val = 0; >> + >> + down_read(&zram->init_lock); >> + if (init_done(zram)) >> + val = atomic64_read(&zram->stats.pages_stored) << PAGE_SHIFT; >> + up_read(&zram->init_lock); >> >> - return scnprintf(buf, PAGE_SIZE, "%llu\n", >> - (u64)(atomic64_read(&zram->stats.pages_stored)) << PAGE_SHIFT); >> + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); >> } >> >> static ssize_t mem_used_total_show(struct device *dev, >> @@ -957,10 +973,6 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, >> struct bio_vec bv; >> >> zram = bdev->bd_disk->private_data; >> - if (!valid_io_request(zram, sector, PAGE_SIZE)) { >> - atomic64_inc(&zram->stats.invalid_io); >> - return -EINVAL; >> - } >> >> down_read(&zram->init_lock); >> if (unlikely(!init_done(zram))) { >> @@ -968,6 +980,13 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, >> goto out_unlock; >> } >> >> + if (!valid_io_request(zram, sector, PAGE_SIZE)) { >> + atomic64_inc(&zram->stats.invalid_io); >> + err = -EINVAL; >> + goto out_unlock; >> + } >> + >> + >> index = sector >> SECTORS_PER_PAGE_SHIFT; >> offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT; >> >> -- >> 1.9.1 >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>