# git rev-parse -q --verify d1dc87763f406d4e67caf16dbe438a5647692395^{commit} d1dc87763f406d4e67caf16dbe438a5647692395 already have revision, skipping fetch # git checkout -q -f -B kisskb d1dc87763f406d4e67caf16dbe438a5647692395 # git clean -qxdf # < git log -1 # commit d1dc87763f406d4e67caf16dbe438a5647692395 # Author: Stephen Brennan # Date: Thu May 19 09:50:30 2022 +0100 # # assoc_array: Fix BUG_ON during garbage collect # # A rare BUG_ON triggered in assoc_array_gc: # # [3430308.818153] kernel BUG at lib/assoc_array.c:1609! # # Which corresponded to the statement currently at line 1593 upstream: # # BUG_ON(assoc_array_ptr_is_meta(p)); # # Using the data from the core dump, I was able to generate a userspace # reproducer[1] and determine the cause of the bug. # # [1]: https://github.com/brenns10/kernel_stuff/tree/master/assoc_array_gc # # After running the iterator on the entire branch, an internal tree node # looked like the following: # # NODE (nr_leaves_on_branch: 3) # SLOT [0] NODE (2 leaves) # SLOT [1] NODE (1 leaf) # SLOT [2..f] NODE (empty) # # In the userspace reproducer, the pr_devel output when compressing this # node was: # # -- compress node 0x5607cc089380 -- # free=0, leaves=0 # [0] retain node 2/1 [nx 0] # [1] fold node 1/1 [nx 0] # [2] fold node 0/1 [nx 2] # [3] fold node 0/2 [nx 2] # [4] fold node 0/3 [nx 2] # [5] fold node 0/4 [nx 2] # [6] fold node 0/5 [nx 2] # [7] fold node 0/6 [nx 2] # [8] fold node 0/7 [nx 2] # [9] fold node 0/8 [nx 2] # [10] fold node 0/9 [nx 2] # [11] fold node 0/10 [nx 2] # [12] fold node 0/11 [nx 2] # [13] fold node 0/12 [nx 2] # [14] fold node 0/13 [nx 2] # [15] fold node 0/14 [nx 2] # after: 3 # # At slot 0, an internal node with 2 leaves could not be folded into the # node, because there was only one available slot (slot 0). Thus, the # internal node was retained. At slot 1, the node had one leaf, and was # able to be folded in successfully. The remaining nodes had no leaves, # and so were removed. By the end of the compression stage, there were 14 # free slots, and only 3 leaf nodes. The tree was ascended and then its # parent node was compressed. When this node was seen, it could not be # folded, due to the internal node it contained. # # The invariant for compression in this function is: whenever # nr_leaves_on_branch < ASSOC_ARRAY_FAN_OUT, the node should contain all # leaf nodes. The compression step currently cannot guarantee this, given # the corner case shown above. # # To fix this issue, retry compression whenever we have retained a node, # and yet nr_leaves_on_branch < ASSOC_ARRAY_FAN_OUT. This second # compression will then allow the node in slot 1 to be folded in, # satisfying the invariant. Below is the output of the reproducer once the # fix is applied: # # -- compress node 0x560e9c562380 -- # free=0, leaves=0 # [0] retain node 2/1 [nx 0] # [1] fold node 1/1 [nx 0] # [2] fold node 0/1 [nx 2] # [3] fold node 0/2 [nx 2] # [4] fold node 0/3 [nx 2] # [5] fold node 0/4 [nx 2] # [6] fold node 0/5 [nx 2] # [7] fold node 0/6 [nx 2] # [8] fold node 0/7 [nx 2] # [9] fold node 0/8 [nx 2] # [10] fold node 0/9 [nx 2] # [11] fold node 0/10 [nx 2] # [12] fold node 0/11 [nx 2] # [13] fold node 0/12 [nx 2] # [14] fold node 0/13 [nx 2] # [15] fold node 0/14 [nx 2] # internal nodes remain despite enough space, retrying # -- compress node 0x560e9c562380 -- # free=14, leaves=1 # [0] fold node 2/15 [nx 0] # after: 3 # # Changes # ======= # DH: # - Use false instead of 0. # - Reorder the inserted lines in a couple of places to put retained before # next_slot. # # ver #2) # - Fix typo in pr_devel, correct comparison to "<=" # # Fixes: 3cb989501c26 ("Add a generic associative array implementation.") # Cc: # Signed-off-by: Stephen Brennan # Signed-off-by: David Howells # cc: Andrew Morton # cc: keyrings@vger.kernel.org # Link: https://lore.kernel.org/r/20220511225517.407935-1-stephen.s.brennan@oracle.com/ # v1 # Link: https://lore.kernel.org/r/20220512215045.489140-1-stephen.s.brennan@oracle.com/ # v2 # Reviewed-by: Jarkko Sakkinen # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/korg/gcc-11.1.0-nolibc/m68k-linux/bin/m68k-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-11.1.0-nolibc/m68k-linux/bin/m68k-linux-ld --version # < git log --format=%s --max-count=1 d1dc87763f406d4e67caf16dbe438a5647692395 # < make -s -j 40 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.1.0-nolibc/m68k-linux/bin/m68k-linux- sun3_defconfig arch/m68k/configs/sun3_defconfig:37:warning: symbol value 'm' invalid for ZPOOL # < make -s -j 40 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.1.0-nolibc/m68k-linux/bin/m68k-linux- help # make -s -j 40 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.1.0-nolibc/m68k-linux/bin/m68k-linux- olddefconfig # make -s -j 40 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.1.0-nolibc/m68k-linux/bin/m68k-linux- In file included from /kisskb/src/include/linux/string.h:20, from /kisskb/src/include/linux/bitmap.h:11, from /kisskb/src/include/linux/cpumask.h:12, from /kisskb/src/include/linux/mm_types_task.h:14, from /kisskb/src/include/linux/mm_types.h:5, from /kisskb/src/include/linux/buildid.h:5, from /kisskb/src/include/linux/module.h:14, from /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:32: In function 'check586', inlined from 'sun3_82586_probe1' at /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:365:6, inlined from 'sun3_82586_probe' at /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:311:8: /kisskb/src/arch/m68k/include/asm/string.h:68:25: warning: '__builtin_memset' offset [0, 11] is out of the bounds [0, 0] [-Warray-bounds] 68 | #define memset(d, c, n) __builtin_memset(d, c, n) | ^~~~~~~~~~~~~~~~~~~~~~~~~ /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:218:9: note: in expansion of macro 'memset' 218 | memset((char *)p->scp,0, sizeof(struct scp_struct)); | ^~~~~~ In file included from /kisskb/src/include/linux/swab.h:5, from /kisskb/src/include/uapi/linux/byteorder/big_endian.h:14, from /kisskb/src/include/linux/byteorder/big_endian.h:5, from /kisskb/src/arch/m68k/include/uapi/asm/byteorder.h:5, from /kisskb/src/include/asm-generic/bitops/le.h:6, from /kisskb/src/arch/m68k/include/asm/bitops.h:529, from /kisskb/src/include/linux/bitops.h:33, from /kisskb/src/include/linux/kernel.h:22, from /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:31: /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c: In function 'sun3_82586_timeout': /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:989:122: warning: array subscript 1 is above array bounds of 'volatile struct transmit_cmd_struct *[1]' [-Warray-bounds] 989 | printk("%s: command-stats: %04x %04x\n",dev->name,swab16(p->xmit_cmds[0]->cmd_status),swab16(p->xmit_cmds[1]->cmd_status)); | ~~~~~~~~~~~~^~~ /kisskb/src/include/uapi/linux/swab.h:107:19: note: in definition of macro '__swab16' 107 | __fswab16(x)) | ^ /kisskb/src/include/linux/printk.h:475:26: note: in expansion of macro 'printk_index_wrap' 475 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__) | ^~~~~~~~~~~~~~~~~ /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:989:17: note: in expansion of macro 'printk' 989 | printk("%s: command-stats: %04x %04x\n",dev->name,swab16(p->xmit_cmds[0]->cmd_status),swab16(p->xmit_cmds[1]->cmd_status)); | ^~~~~~ /kisskb/src/drivers/net/ethernet/i825xx/sun3_82586.c:155:46: note: while referencing 'xmit_cmds' 155 | volatile struct transmit_cmd_struct *xmit_cmds[NUM_XMIT_BUFFS]; | ^~~~~~~~~ Completed OK # rm -rf /kisskb/build/linus_sun3_defconfig_m68k-gcc11 # Build took: 0:01:01.830056