The patch titled
Subject: zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2
has been added to the -mm tree. Its filename is
zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2.patch
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------------------------------------------------------
From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2
- description correction - Andrew
- add comment about removing BDI_CAP_SYNCHRONOUS_IO
Link: https://lore.kernel.org/lkml/0516ae2d-b0fd-92c5-aa92-112ba7bd32fc@xxxxxxxxxx/
Link: http://lkml.kernel.org/r/20180802051112.86174-1-minchan@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20180805233722.217347-1-minchan@xxxxxxxxxx
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Reported-by: Tino Lehnig <tino.lehnig@xxxxxxxxxx>
Tested-by: Tino Lehnig <tino.lehnig@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.15+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN drivers/block/zram/zram_drv.c~zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2 drivers/block/zram/zram_drv.c
--- a/drivers/block/zram/zram_drv.c~zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2
+++ a/drivers/block/zram/zram_drv.c
@@ -401,6 +401,16 @@ static ssize_t backing_dev_store(struct
zram->backing_dev = backing_dev;
zram->bitmap = bitmap;
zram->nr_pages = nr_pages;
+ /*
+ * With writeback feature, zram does asynchronous IO so it's no longer
+ * synchronous device so let's remove synchronous io flag. Othewise,
+ * upper layer(e.g., swap) could wait IO completion rather than
+ * (submit and return), which will cause system sluggish.
+ * Furthermore, when the IO function returns(e.g., swap_readpage),
+ * upper layer expects IO was done so it could deallocate the page
+ * freely but in fact, IO is going on so finally could cause
+ * use-after-free when the IO is really done.
+ */
zram->disk->queue->backing_dev_info->capabilities &=
~BDI_CAP_SYNCHRONOUS_IO;
up_write(&zram->init_lock);
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
zram-remove-bd_cap_synchronous_io-with-writeback-feature.patch
zram-remove-bd_cap_synchronous_io-with-writeback-feature-v2.patch
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