6.16-stable review patch. If anyone has any objections, please let me know.
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From: Sergey Senozhatsky senozhatsky@chromium.org
commit ce4be9e4307c5a60701ff6e0cafa74caffdc54ce upstream.
Parallel concurrent writes to the same zram index result in leaked zsmalloc handles. Schematically we can have something like this:
CPU0 CPU1 zram_slot_lock() zs_free(handle) zram_slot_lock() zram_slot_lock() zs_free(handle) zram_slot_lock()
compress compress handle = zs_malloc() handle = zs_malloc() zram_slot_lock zram_set_handle(handle) zram_slot_lock zram_slot_lock zram_set_handle(handle) zram_slot_lock
Either CPU0 or CPU1 zsmalloc handle will leak because zs_free() is done too early. In fact, we need to reset zram entry right before we set its new handle, all under the same slot lock scope.
Link: https://lkml.kernel.org/r/20250909045150.635345-1-senozhatsky@chromium.org Fixes: 71268035f5d7 ("zram: free slot memory early during write") Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org Reported-by: Changhui Zhong czhong@redhat.com Closes: https://lore.kernel.org/all/CAGVVp+UtpGoW5WEdEU7uVTtsSCjPN=ksN6EcvyypAtFDOUf... Tested-by: Changhui Zhong czhong@redhat.com Cc: Jens Axboe axboe@kernel.dk Cc: Minchan Kim minchan@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/zram/zram_drv.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)
--- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1794,6 +1794,7 @@ static int write_same_filled_page(struct u32 index) { zram_slot_lock(zram, index); + zram_free_page(zram, index); zram_set_flag(zram, index, ZRAM_SAME); zram_set_handle(zram, index, fill); zram_slot_unlock(zram, index); @@ -1831,6 +1832,7 @@ static int write_incompressible_page(str kunmap_local(src);
zram_slot_lock(zram, index); + zram_free_page(zram, index); zram_set_flag(zram, index, ZRAM_HUGE); zram_set_handle(zram, index, handle); zram_set_obj_size(zram, index, PAGE_SIZE); @@ -1854,11 +1856,6 @@ static int zram_write_page(struct zram * unsigned long element; bool same_filled;
- /* First, free memory allocated to this slot (if any) */ - zram_slot_lock(zram, index); - zram_free_page(zram, index); - zram_slot_unlock(zram, index); - mem = kmap_local_page(page); same_filled = page_same_filled(mem, &element); kunmap_local(mem); @@ -1900,6 +1897,7 @@ static int zram_write_page(struct zram * zcomp_stream_put(zstrm);
zram_slot_lock(zram, index); + zram_free_page(zram, index); zram_set_handle(zram, index, handle); zram_set_obj_size(zram, index, comp_len); zram_slot_unlock(zram, index);