pm24.git/drivers/block/zram, branch master

zram: fix NULL pointer in comp_algorithm_show()

2024-11-15T06:49:19Z

LTP reported a NULL pointer dereference as followed: CPU: 7 UID: 0 PID: 5995 Comm: cat Kdump: loaded Not tainted 6.12.0-rc6+ #3 Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : __pi_strcmp+0x24/0x140 lr : zcomp_available_show+0x60/0x100 [zram] sp : ffff800088b93b90 x29: ffff800088b93b90 x28: 0000000000000001 x27: 0000000000400cc0 x26: 0000000000000ffe x25: ffff80007b3e2388 x24: 0000000000000000 x23: ffff80007b3e2390 x22: ffff0004041a9000 x21: ffff80007b3e2900 x20: 0000000000000000 x19: 0000000000000000 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: ffff80007b3e2900 x9 : ffff80007b3cb280 x8 : 0101010101010101 x7 : 0000000000000000 x6 : 0000000000000000 x5 : 0000000000000040 x4 : 0000000000000000 x3 : 00656c722d6f7a6c x2 : 0000000000000000 x1 : ffff80007b3e2900 x0 : 0000000000000000 Call trace: __pi_strcmp+0x24/0x140 comp_algorithm_show+0x40/0x70 [zram] dev_attr_show+0x28/0x80 sysfs_kf_seq_show+0x90/0x140 kernfs_seq_show+0x34/0x48 seq_read_iter+0x1d4/0x4e8 kernfs_fop_read_iter+0x40/0x58 new_sync_read+0x9c/0x168 vfs_read+0x1a8/0x1f8 ksys_read+0x74/0x108 __arm64_sys_read+0x24/0x38 invoke_syscall+0x50/0x120 el0_svc_common.constprop.0+0xc8/0xf0 do_el0_svc+0x24/0x38 el0_svc+0x38/0x138 el0t_64_sync_handler+0xc0/0xc8 el0t_64_sync+0x188/0x190 The zram->comp_algs[ZRAM_PRIMARY_COMP] can be NULL in zram_add() if comp_algorithm_set() has not been called. User can access the zram device by sysfs after device_add_disk(), so there is a time window to trigger the NULL pointer dereference. Move it ahead device_add_disk() to make sure when user can access the zram device, it is ready. comp_algorithm_set() is protected by zram->init_lock in other places and no such problem. Link: https://lkml.kernel.org/r/20241108100147.3776123-1-liushixin2@huawei.com Fixes: 7ac07a26dea7 ("zram: preparation for multi-zcomp support") Signed-off-by: Liu Shixin Reviewed-by: Sergey Senozhatsky Cc: Jens Axboe Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: ZRAM_DEF_COMP should depend on ZRAM

2024-11-12T01:22:27Z

When Compressed RAM block device support is disabled, the CONFIG_ZRAM_DEF_COMP symbol still ends up in the generated config file: CONFIG_ZRAM_DEF_COMP="unset-value" While this causes no real harm, avoid polluting the config file by adding a dependency on ZRAM. Link: https://lkml.kernel.org/r/64e05bad68a9bd5cc322efd114a04d25de525940.1730807319.git.geert@linux-m68k.org Fixes: 917a59e81c34 ("zram: introduce custom comp backends API") Signed-off-by: Geert Uytterhoeven Reviewed-by: Sergey Senozhatsky Cc: Jens Axboe Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: clear IDLE flag in mark_idle()

2024-11-11T21:09:35Z

If entry does not fulfill current mark_idle() parameters, e.g. cutoff time, then we should clear its ZRAM_IDLE from previous mark_idle() invocations. Consider the following case: - mark_idle() cutoff time 8h - mark_idle() cutoff time 4h - writeback() idle - will writeback entries with cutoff time 8h, while it should only pick entries with cutoff time 4h The bug was reported by Shin Kawamura. Link: https://lkml.kernel.org/r/20241028153629.1479791-3-senozhatsky@chromium.org Fixes: 755804d16965 ("zram: introduce an aged idle interface") Signed-off-by: Sergey Senozhatsky Reported-by: Shin Kawamura Acked-by: Brian Geffon Cc: Minchan Kim Signed-off-by: Andrew Morton Cc:

zram: clear IDLE flag after recompression

2024-11-11T21:09:12Z

Patch series "zram: IDLE flag handling fixes", v2. zram can wrongly preserve ZRAM_IDLE flag on its entries which can result in premature post-processing (writeback and recompression) of such entries. This patch (of 2) Recompression should clear ZRAM_IDLE flag on the entries it has accessed, because otherwise some entries, specifically those for which recompression has failed, become immediate candidate entries for another post-processing (e.g. writeback). Consider the following case: - recompression marks entries IDLE every 4 hours and attempts to recompress them - some entries are incompressible, so we keep them intact and hence preserve IDLE flag - writeback marks entries IDLE every 8 hours and writebacks IDLE entries, however we have IDLE entries left from recompression, so writeback prematurely writebacks those entries. The bug was reported by Shin Kawamura. Link: https://lkml.kernel.org/r/20241028153629.1479791-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20241028153629.1479791-2-senozhatsky@chromium.org Fixes: 84b33bf78889 ("zram: introduce recompress sysfs knob") Signed-off-by: Sergey Senozhatsky Reported-by: Shin Kawamura Acked-by: Brian Geffon Cc: Minchan Kim Signed-off-by: Andrew Morton Cc:

zram: do not open-code comp priority 0

2024-11-07T04:11:11Z

A cosmetic change: do not open-code compression priority 0, use ZRAM_PRIMARY_COMP instead. Link: https://lkml.kernel.org/r/20241009042908.750260-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: remove UNDER_WB and simplify writeback

2024-11-06T00:56:23Z

We now have only one active post-processing at any time, so we don't have same race conditions that we had before. If slot selected for post-processing gets freed or freed and reallocated it loses its PP_SLOT flag and there is no way for such a slot to gain PP_SLOT flag again until current post-processing terminates. Link: https://lkml.kernel.org/r/20240917021020.883356-8-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: reshuffle zram_free_page() flags operations

2024-11-06T00:56:23Z

Drop some redundant zram_test_flag() calls and re-order zram_clear_flag() calls. Plus two small trivial coding style fixes. No functional changes. Link: https://lkml.kernel.org/r/20240917021020.883356-7-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: do not mark idle slots that cannot be idle

2024-11-06T00:56:22Z

ZRAM_SAME slots cannot be post-processed (writeback or recompress) so do not mark them ZRAM_IDLE. Same with ZRAM_WB slots, they cannot be ZRAM_IDLE because they are not in zsmalloc pool anymore. Link: https://lkml.kernel.org/r/20240917021020.883356-6-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: rework writeback target selection strategy

2024-11-06T00:56:22Z

Writeback suffers from the same problem as recompression did before - target slot selection for writeback is just a simple iteration over zram->table entries (stored pages) which selects suboptimal targets for writeback. This is especially problematic for writeback, because we uncompress objects before writeback so each of them takes 4K out of limited writeback storage. For example, when we take a 48 bytes slot and store it as a 4K object to writeback device we only save 48 bytes of memory (release from zsmalloc pool). We naturally want to pick the largest objects for writeback, because then each writeback will release the largest amount of memory. This patch applies the same solution and strategy as for recompression target selection: pp control (post-process) with 16 buckets of candidate pp slots. Slots are assigned to pp buckets based on sizes - the larger the slot the higher the group index. This gives us sorted by size lists of candidate slots (in linear time), so that among post-processing candidate slots we always select the largest ones first and maximize the memory saving. TEST ==== A very simple demonstration: zram is configured with a writeback device. A limited writeback (wb_limit 2500 pages) is performed then, with a log of sizes of slots that were written back. You can see that patched zram selects slots for recompression in significantly different manner, which leads to higher memory savings (see column #2 of mm_stat output). BASE ---- *** initial state of zram device /sys/block/zram0/mm_stat 1750327296 619765836 631902208 0 631902208 1 0 34278 34278 *** writeback idle wb_limit 2500 /sys/block/zram0/mm_stat 1750327296 617622333 631578624 0 631902208 1 0 34278 34278 Sizes of selected objects for writeback: ... 193 349 46 46 46 46 852 1002 543 162 107 49 34 34 34 ... PATCHED ------- *** initial state of zram device /sys/block/zram0/mm_stat 1750319104 619760957 631992320 0 631992320 1 0 34278 34278 *** writeback idle wb_limit 2500 /sys/block/zram0/mm_stat 1750319104 612672056 626135040 0 631992320 1 0 34278 34278 Sizes of selected objects for writeback: ... 3667 3580 3581 3580 3581 3581 3581 3231 3211 3203 3231 3246 ... Note, pp-slots are not strictly sorted, there is a PP_BUCKET_SIZE_RANGE variation of sizes within particular bucket. Link: https://lkml.kernel.org/r/20240917021020.883356-5-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: rework recompress target selection strategy

2024-11-06T00:56:22Z

Target slot selection for recompression is just a simple iteration over zram->table entries (stored pages) from slot 0 to max slot. Given that zram->table slots are written in random order and are not sorted by size, a simple iteration over slots selects suboptimal targets for recompression. This is not a problem if we recompress every single zram->table slot, but we never do that in reality. In reality we limit the number of slots we can recompress (via max_pages parameter) and hence proper slot selection becomes very important. The strategy is quite simple, suppose we have two candidate slots for recompression, one of size 48 bytes and one of size 2800 bytes, and we can recompress only one, then it certainly makes more sense to pick 2800 entry for recompression. Because even if we manage to compress 48 bytes objects even further the savings are going to be very small. Potential savings after good re-compression of 2800 bytes objects are much higher. This patch reworks slot selection and introduces the strategy described above: among candidate slots always select the biggest ones first. For that the patch introduces zram_pp_ctl (post-processing) structure which holds NUM_PP_BUCKETS pp buckets of slots. Slots are assigned to a particular group based on their sizes - the larger the size of the slot the higher the group index. This, basically, sorts slots by size in liner time (we still perform just one iteration over zram->table slots). When we select slot for recompression we always first lookup in higher pp buckets (those that hold the largest slots). Which achieves the desired behavior. TEST ==== A very simple demonstration: zram is configured with zstd, and zstd with dict as a recompression stream. A limited (max 4096 pages) recompression is performed then, with a log of sizes of slots that were recompressed. You can see that patched zram selects slots for recompression in significantly different manner, which leads to higher memory savings (see column #2 of mm_stat output). BASE ---- *** initial state of zram device /sys/block/zram0/mm_stat 1750994944 504491413 514203648 0 514203648 1 0 34204 34204 *** recompress idle max_pages=4096 /sys/block/zram0/mm_stat 1750994944 504262229 514953216 0 514203648 1 0 34204 34204 Sizes of selected objects for recompression: ... 45 58 24 226 91 40 24 24 24 424 2104 93 2078 2078 2078 959 154 ... PATCHED ------- *** initial state of zram device /sys/block/zram0/mm_stat 1750982656 504492801 514170880 0 514170880 1 0 34204 34204 *** recompress idle max_pages=4096 /sys/block/zram0/mm_stat 1750982656 503716710 517586944 0 514170880 1 0 34204 34204 Sizes of selected objects for recompression: ... 3680 3694 3667 3590 3614 3553 3537 3548 3550 3542 3543 3537 ... Note, pp-slots are not strictly sorted, there is a PP_BUCKET_SIZE_RANGE variation of sizes within particular bucket. [senozhatsky@chromium.org: do not skip the first bucket] Link: https://lkml.kernel.org/r/20241001085634.1948384-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20240917021020.883356-4-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Cc: Dan Carpenter Signed-off-by: Andrew Morton