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Subject[PATCH 1/2] Staging: zram: Turn lockdep off during zram_init_device()

zram->init_lock can be hold over an allocation that may try to reclaim
memory in zram_init_device(). The same lock can later be taken from a
reclaim context in zram_make_request(), thus triggering a lockdep
warning. However, memory can not be reclaimed to an uninitialized zram
device. Therefore, this warning is a false positive.
To prevent the warning to occur, we turn lockdep off during while the
device is initialized.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Reported-by: Witold Baryluk <baryluk@smp.if.uj.edu.pl>
---
zram_drv.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 09de99f..34f4b96 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -637,10 +637,22 @@ int zram_init_device(struct zram *zram)
int ret;
size_t num_pages;

+ /*
+ * Here we hold init_lock over allocations that may try to reclaim
+ * memory. The same lock is also taken from a reclaim context in
+ * zram_make_request(). That end up in a lockdep warning.
+ * Moreover the table can be quite big an it wouldn't be reasonable to
+ * use kmalloc(GFP_NOFS,...) to allocate it.
+ * Fortunately, memory can not be reclaimed to an uninitialized zram
+ * device, so this warning is a false positive. Therefore, to prevent
+ * the warning, we turn lockdep off here.
+ */
+ lockdep_off();
down_write(&zram->init_lock);

if (zram->init_done) {
up_write(&zram->init_lock);
+ lockdep_on();
return 0;
}

@@ -682,6 +694,7 @@ int zram_init_device(struct zram *zram)

zram->init_done = 1;
up_write(&zram->init_lock);
+ lockdep_on();

pr_debug("Initialization done!\n");
return 0;
@@ -692,6 +705,7 @@ fail_no_table:
fail:
__zram_reset_device(zram);
up_write(&zram->init_lock);
+ lockdep_on();
pr_err("Initialization failed: err=%d\n", ret);
return ret;
}

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