Re: + zram-add-dynamic-device-add-remove-functionality.patch added to -mm tree

From: Minchan Kim
Date: Wed May 06 2015 - 00:48:35 EST

Hello Sergey,

While I test this patch, I got this warning.
I used attached script to reproduce it.
You should run several copy of script to reproduce it like below.

#>./dynamic_remove.sh &
#>./dynamic_remove.sh &

Hope you investigate the problem.

...
...

[ OK ]
* Starting MD monitoring service mdadm --monitor 
[ OK ]
* Checking battery state...  grep: /sys/power/state: No such file or directory
grep: /sys/power/state: No such file or directory
grep: /sys/power/state: No such file or directory

[ OK ]
[ 10.961394] init: plymouth-stop pre-start process (1441) terminated with status 1
[ 11.655424] random: nonblocking pool is initialized
[ 98.106916] zram: Added device: zram1
[ 98.108124] zram1: detected capacity change from 0 to 20971520
[ 98.111037] zram: Added device: zram2
[ 98.112876] zram2: detected capacity change from 0 to 20971520
[ 98.118034] zram: Added device: zram3
[ 98.119691] zram3: detected capacity change from 0 to 20971520
[ 98.123948] zram: Added device: zram4
[ 98.125205] zram4: detected capacity change from 0 to 20971520
[ 98.129088] zram: Added device: zram5
[ 98.129998] zram5: detected capacity change from 0 to 20971520
[ 98.133486] zram: Added device: zram6
[ 98.134579] zram6: detected capacity change from 0 to 20971520
[ 98.138140] zram: Added device: zram7
[ 98.140175] zram7: detected capacity change from 0 to 20971520
[ 98.143433] zram: Added device: zram8
[ 98.144389] zram8: detected capacity change from 0 to 20971520
[ 98.147172] zram: Added device: zram9
[ 98.148574] zram9: detected capacity change from 0 to 20971520
[ 98.151807] zram: Added device: zram10
[ 98.153247] zram10: detected capacity change from 0 to 20971520
[ 98.158626] zram: Added device: zram11
[ 98.159785] zram11: detected capacity change from 0 to 20971520
[ 98.163183] zram: Added device: zram12
[ 98.165138] zram12: detected capacity change from 0 to 20971520
[ 98.168077] zram: Added device: zram13
[ 98.169060] zram13: detected capacity change from 0 to 20971520
[ 98.172264] zram: Added device: zram14
[ 98.173445] zram14: detected capacity change from 0 to 20971520
[ 98.176820] zram: Added device: zram15
[ 98.177804] zram15: detected capacity change from 0 to 20971520
[ 98.180816] zram: Added device: zram16
[ 98.182020] zram16: detected capacity change from 0 to 20971520
[ 98.185495] zram: Added device: zram17
[ 98.187245] zram17: detected capacity change from 0 to 20971520
[ 98.191791] zram: Added device: zram18
[ 98.192925] zram18: detected capacity change from 0 to 20971520
[ 98.196314] zram: Added device: zram19
[ 98.198937] zram19: detected capacity change from 0 to 20971520
[ 98.202523] zram: Added device: zram20
[ 98.203615] zram20: detected capacity change from 0 to 20971520
[ 98.207473] zram: Added device: zram21
[ 98.208529] zram21: detected capacity change from 0 to 20971520
[ 98.211940] zram: Added device: zram22
[ 98.212839] zram22: detected capacity change from 0 to 20971520
[ 98.216381] zram: Added device: zram23
[ 98.217278] zram23: detected capacity change from 0 to 20971520
[ 98.219953] zram: Added device: zram24
[ 98.222805] zram24: detected capacity change from 0 to 20971520
[ 98.226039] zram: Added device: zram25
[ 98.227008] zram25: detected capacity change from 0 to 20971520
[ 98.246547] zram: Removed device: zram4
[ 98.316665] zram: Removed device: zram8
[ 98.330010] zram: Removed device: zram1
[ 98.364826] zram: Removed device: zram3
[ 98.393897] zram: Removed device: zram5
[ 98.395801] zram: Removed device: zram6
[ 98.399364] zram: Removed device: zram7
[ 98.405376] zram: Removed device: zram11
[ 98.408452] zram: Removed device: zram12
[ 98.420747] zram: Removed device: zram14
[ 98.433739] zram: Removed device: zram15
[ 98.447536] zram: Removed device: zram16
[ 98.450580] zram: Removed device: zram17
[ 98.457826] zram: Removed device: zram18
[ 98.459562] zram: Removed device: zram19
[ 98.461362] zram: Removed device: zram20
[ 98.463272] zram: Removed device: zram21
[ 98.464454] zram: Removed device: zram22
[ 98.465547] zram: Removed device: zram23
[ 98.466794] zram: Removed device: zram24
[ 98.467938] zram: Removed device: zram25
[ 98.470475] zram: Removed device: zram2
[ 98.472080] zram: Removed device: zram9
[ 98.473410] zram: Removed device: zram10
[ 98.474974] zram: Removed device: zram13
[ 98.480408] zram: Added device: zram1
[ 98.481656] zram1: detected capacity change from 0 to 20971520
[ 98.484709] zram: Added device: zram2
[ 98.485533] zram2: detected capacity change from 0 to 20971520
[ 98.490166] zram: Added device: zram3
[ 98.491463] zram3: detected capacity change from 0 to 20971520
[ 98.495471] zram: Added device: zram4
[ 98.496793] zram4: detected capacity change from 0 to 20971520
[ 98.499398] zram: Added device: zram5
[ 98.500522] zram5: detected capacity change from 0 to 20971520
[ 98.507491] zram: Added device: zram6
[ 98.508370] zram6: detected capacity change from 0 to 20971520
[ 98.518639] zram: Added device: zram7
[ 98.519697] zram7: detected capacity change from 0 to 20971520
[ 98.522650] zram: Added device: zram8
[ 98.523507] zram8: detected capacity change from 0 to 20971520
[ 98.525985] zram: Added device: zram9
[ 98.527046] zram9: detected capacity change from 0 to 20971520
[ 98.531154] zram: Added device: zram10
[ 98.532390] zram10: detected capacity change from 0 to 20971520
[ 98.535335] zram: Added device: zram11
[ 98.536179] zram11: detected capacity change from 0 to 20971520
[ 98.538633] zram: Added device: zram12
[ 98.539812] zram12: detected capacity change from 0 to 20971520
[ 98.545105] zram: Added device: zram13
[ 98.546696] zram13: detected capacity change from 0 to 20971520
[ 98.550453] zram: Added device: zram14
[ 98.551394] zram14: detected capacity change from 0 to 20971520
[ 98.556193] zram: Added device: zram15
[ 98.557564] zram15: detected capacity change from 0 to 20971520
[ 98.561741] zram: Added device: zram16
[ 98.562799] zram16: detected capacity change from 0 to 20971520
[ 98.565537] zram: Added device: zram17
[ 98.566344] zram17: detected capacity change from 0 to 20971520
[ 98.569192] zram: Added device: zram18
[ 98.570437] zram18: detected capacity change from 0 to 20971520
[ 98.573588] zram: Added device: zram19
[ 98.574826] zram19: detected capacity change from 0 to 20971520
[ 98.578450] zram: Added device: zram20
[ 98.579623] zram20: detected capacity change from 0 to 20971520
[ 98.582528] zram: Added device: zram21
[ 98.584440] zram21: detected capacity change from 0 to 20971520
[ 98.587922] zram: Added device: zram22
[ 98.589239] zram22: detected capacity change from 0 to 20971520
[ 98.593854] zram: Added device: zram23
[ 98.595130] zram23: detected capacity change from 0 to 20971520
[ 98.598610] zram: Added device: zram24
[ 98.599953] zram24: detected capacity change from 0 to 20971520
[ 98.603456] zram: Added device: zram25
[ 98.604706] zram25: detected capacity change from 0 to 20971520
[ 98.631424] zram: Removed device: zram11
[ 98.639214] zram: Removed device: zram14
[ 98.647116] zram: Removed device: zram15
[ 98.756017] zram: Removed device: zram2
[ 98.757087] ------------[ cut here ]------------
[ 98.758349] WARNING: CPU: 5 PID: 2952 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x68/0x80()
[ 98.760065] sysfs: cannot create duplicate filename '/devices/virtual/bdi/252:2'
[ 98.761061] Modules linked in:
[ 98.761530] CPU: 5 PID: 2952 Comm: cat Not tainted 4.1.0-rc2-next-20150505+ #1260
[ 98.762682] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[ 98.764140] ffff88005d40f948 ffff88005d40f948 ffffffff8163d8d8 0000000000000000
[ 98.765614] ffff88005d40f998 ffff88005d40f988 ffffffff8105f02a 0000000000000000
[ 98.766815] ffff8800653c2000 ffff88007f526210 ffff88004b3aa1c8 ffff880065799360
[ 98.768980] Call Trace:
[ 98.769643] [<ffffffff8163d8d8>] dump_stack+0x4c/0x65
[ 98.770431] [<ffffffff8105f02a>] warn_slowpath_common+0x8a/0xc0
[ 98.771353] [<ffffffff8105f0a6>] warn_slowpath_fmt+0x46/0x50
[ 98.772220] [<ffffffff8105f065>] ? warn_slowpath_fmt+0x5/0x50
[ 98.773099] [<ffffffff8126d748>] sysfs_warn_dup+0x68/0x80
[ 98.773903] [<ffffffff8126d6e5>] ? sysfs_warn_dup+0x5/0x80
[ 98.774750] [<ffffffff8126d7ee>] sysfs_create_dir_ns+0x8e/0xa0
[ 98.775794] [<ffffffff8126d765>] ? sysfs_create_dir_ns+0x5/0xa0
[ 98.776672] [<ffffffff813710d5>] kobject_add_internal+0xa5/0x2f0
[ 98.777737] [<ffffffff81644133>] ? __mutex_unlock_slowpath+0xb3/0x180
[ 98.778765] [<ffffffff81371500>] kobject_add+0x60/0xb0
[ 98.779598] [<ffffffff81465fe5>] ? get_device_parent+0x5/0x200
[ 98.780430] [<ffffffff81466552>] device_add+0x102/0x5b0
[ 98.780956] [<ffffffff81466455>] ? device_add+0x5/0x5b0
[ 98.781513] [<ffffffff81466c18>] device_create_groups_vargs+0xd8/0x100
[ 98.782119] [<ffffffff81466c45>] ? device_create_vargs+0x5/0x20
[ 98.782851] [<ffffffff81466c5c>] device_create_vargs+0x1c/0x20
[ 98.783464] [<ffffffff81198e37>] bdi_register+0x67/0x2a0
[ 98.784081] [<ffffffff81199075>] ? bdi_register_dev+0x5/0x30
[ 98.784609] [<ffffffff81199097>] bdi_register_dev+0x27/0x30
[ 98.785139] [<ffffffff81359f29>] add_disk+0x1b9/0x4e0
[ 98.785844] [<ffffffff8137a9a4>] ? snprintf+0x34/0x40
[ 98.786353] [<ffffffff814867cc>] zram_add+0x1ec/0x2f0
[ 98.786833] [<ffffffff814868f2>] zram_add_show+0x22/0x60
[ 98.787344] [<ffffffff81469edb>] class_attr_show+0x1b/0x30
[ 98.787848] [<ffffffff8126d1ff>] sysfs_kf_seq_show+0xcf/0x1d0
[ 98.788374] [<ffffffff8126b716>] kernfs_seq_show+0x26/0x30
[ 98.788880] [<ffffffff8120eaf5>] seq_read+0xf5/0x3a0
[ 98.789338] [<ffffffff8126c040>] ? kernfs_vma_page_mkwrite+0xa0/0xa0
[ 98.789917] [<ffffffff8126c165>] kernfs_fop_read+0x125/0x180
[ 98.790483] [<ffffffff811e5c98>] __vfs_read+0x28/0xe0
[ 98.790959] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.791476] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.791952] [<ffffffff811e62e6>] vfs_read+0x86/0x140
[ 98.792418] [<ffffffff81207fa7>] ? __fdget_pos+0x17/0x50
[ 98.792908] [<ffffffff811e7179>] SyS_read+0x49/0xb0
[ 98.793360] [<ffffffff81646f97>] system_call_fastpath+0x12/0x6f
[ 98.793903] ---[ end trace e1035d8c51ec986c ]---
[ 98.794358] ------------[ cut here ]------------
[ 98.794783] WARNING: CPU: 5 PID: 2952 at lib/kobject.c:240 kobject_add_internal+0x284/0x2f0()
[ 98.795999] kobject_add_internal failed for 252:2 with -EEXIST, don't try to register things with the same name in the same directory.
[ 98.797097] Modules linked in:
[ 98.797396] CPU: 5 PID: 2952 Comm: cat Tainted: G W 4.1.0-rc2-next-20150505+ #1260
[ 98.798173] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[ 98.798951] ffff88005d40f9a8 ffff88005d40f9a8 ffffffff8163d8d8 0000000000000000
[ 98.799689] ffff88005d40f9f8 ffff88005d40f9e8 ffffffff8105f02a 0000000000000000
[ 98.800383] ffff88007f64a410 ffff880065799360 00000000ffffffef ffff880065799360
[ 98.801096] Call Trace:
[ 98.801330] [<ffffffff8163d8d8>] dump_stack+0x4c/0x65
[ 98.801800] [<ffffffff8105f02a>] warn_slowpath_common+0x8a/0xc0
[ 98.802383] [<ffffffff8105f0a6>] warn_slowpath_fmt+0x46/0x50
[ 98.802908] [<ffffffff813708b6>] ? kobj_kset_leave+0x46/0x60
[ 98.803437] [<ffffffff8105f065>] ? warn_slowpath_fmt+0x5/0x50
[ 98.803967] [<ffffffff813712b4>] kobject_add_internal+0x284/0x2f0
[ 98.804662] [<ffffffff81644133>] ? __mutex_unlock_slowpath+0xb3/0x180
[ 98.805255] [<ffffffff81371500>] kobject_add+0x60/0xb0
[ 98.805734] [<ffffffff81465fe5>] ? get_device_parent+0x5/0x200
[ 98.806273] [<ffffffff81466552>] device_add+0x102/0x5b0
[ 98.806790] [<ffffffff81466455>] ? device_add+0x5/0x5b0
[ 98.807404] [<ffffffff81466c18>] device_create_groups_vargs+0xd8/0x100
[ 98.808039] [<ffffffff81466c45>] ? device_create_vargs+0x5/0x20
[ 98.808595] [<ffffffff81466c5c>] device_create_vargs+0x1c/0x20
[ 98.809120] [<ffffffff81198e37>] bdi_register+0x67/0x2a0
[ 98.809604] [<ffffffff81199075>] ? bdi_register_dev+0x5/0x30
[ 98.810101] [<ffffffff81199097>] bdi_register_dev+0x27/0x30
[ 98.810685] [<ffffffff81359f29>] add_disk+0x1b9/0x4e0
[ 98.811155] [<ffffffff8137a9a4>] ? snprintf+0x34/0x40
[ 98.811616] [<ffffffff814867cc>] zram_add+0x1ec/0x2f0
[ 98.812069] [<ffffffff814868f2>] zram_add_show+0x22/0x60
[ 98.812550] [<ffffffff81469edb>] class_attr_show+0x1b/0x30
[ 98.813076] [<ffffffff8126d1ff>] sysfs_kf_seq_show+0xcf/0x1d0
[ 98.813592] [<ffffffff8126b716>] kernfs_seq_show+0x26/0x30
[ 98.814069] [<ffffffff8120eaf5>] seq_read+0xf5/0x3a0
[ 98.814599] [<ffffffff8126c040>] ? kernfs_vma_page_mkwrite+0xa0/0xa0
[ 98.815179] [<ffffffff8126c165>] kernfs_fop_read+0x125/0x180
[ 98.815716] [<ffffffff811e5c98>] __vfs_read+0x28/0xe0
[ 98.816153] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.816601] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.817051] [<ffffffff811e62e6>] vfs_read+0x86/0x140
[ 98.817485] [<ffffffff81207fa7>] ? __fdget_pos+0x17/0x50
[ 98.817950] [<ffffffff811e7179>] SyS_read+0x49/0xb0
[ 98.818455] [<ffffffff81646f97>] system_call_fastpath+0x12/0x6f
[ 98.818985] ---[ end trace e1035d8c51ec986d ]---
[ 98.819810] BUG: unable to handle kernel NULL pointer dereference at 0000000000000040
[ 98.820591] IP: [<ffffffff8126da50>] sysfs_do_create_link_sd.isra.2+0x40/0xd0
[ 98.821290] PGD 61669067 PUD 61553067 PMD 0
[ 98.821709] Oops: 0000 [#1] SMP
[ 98.822047] Dumping ftrace buffer:
[ 98.822425] (ftrace buffer empty)
[ 98.822763] Modules linked in:
[ 98.823056] CPU: 5 PID: 2952 Comm: cat Tainted: G W 4.1.0-rc2-next-20150505+ #1260
[ 98.823663] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[ 98.823663] task: ffff880056942140 ti: ffff88005d40c000 task.ti: ffff88005d40c000
[ 98.823663] RIP: 0010:[<ffffffff8126da50>] [<ffffffff8126da50>] sysfs_do_create_link_sd.isra.2+0x40/0xd0
[ 98.823663] RSP: 0018:ffff88005d40fc28 EFLAGS: 00010292
[ 98.823663] RAX: ffff880056942140 RBX: 0000000000000040 RCX: 0000000006da06d9
[ 98.823663] RDX: 0000000006d906d9 RSI: 1ca0f28c302c6000 RDI: ffffffff81c82ca0
[ 98.823663] RBP: ffff88005d40fc58 R08: 0000000000000001 R09: 0000000000000000
[ 98.823663] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff819f9187
[ 98.823663] R13: ffff880061ca2688 R14: 0000000000000001 R15: ffff88007f64c490
[ 98.823663] FS: 00007f1262ed4700(0000) GS:ffff880068140000(0000) knlGS:0000000000000000
[ 98.823663] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 98.823663] CR2: 0000000000000040 CR3: 000000005fc77000 CR4: 00000000000007e0
[ 98.823663] Stack:
[ 98.823663] ffffffff8135931b ffff88007f64c400 ffff88007f64c4a0 ffff88005f889660
[ 98.823663] ffff88007f64c40c ffff88007f64c490 ffff88005d40fc68 ffffffff8126db05
[ 98.823663] ffff88005d40fcd8 ffffffff81359fc2 ffff88007f64c400 ffffffff8137a9a4
[ 98.823663] Call Trace:
[ 98.823663] [<ffffffff8135931b>] ? disk_part_iter_next+0x2b/0x280
[ 98.823663] [<ffffffff8126db05>] sysfs_create_link+0x25/0x50
[ 98.823663] [<ffffffff81359fc2>] add_disk+0x252/0x4e0
[ 98.823663] [<ffffffff8137a9a4>] ? snprintf+0x34/0x40
[ 98.823663] [<ffffffff814867cc>] zram_add+0x1ec/0x2f0
[ 98.823663] [<ffffffff814868f2>] zram_add_show+0x22/0x60
[ 98.823663] [<ffffffff81469edb>] class_attr_show+0x1b/0x30
[ 98.823663] [<ffffffff8126d1ff>] sysfs_kf_seq_show+0xcf/0x1d0
[ 98.823663] [<ffffffff8126b716>] kernfs_seq_show+0x26/0x30
[ 98.823663] [<ffffffff8120eaf5>] seq_read+0xf5/0x3a0
[ 98.823663] [<ffffffff8126c040>] ? kernfs_vma_page_mkwrite+0xa0/0xa0
[ 98.823663] [<ffffffff8126c165>] kernfs_fop_read+0x125/0x180
[ 98.823663] [<ffffffff811e5c98>] __vfs_read+0x28/0xe0
[ 98.823663] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.823663] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.823663] [<ffffffff811e62e6>] vfs_read+0x86/0x140
[ 98.823663] [<ffffffff81207fa7>] ? __fdget_pos+0x17/0x50
[ 98.823663] [<ffffffff811e7179>] SyS_read+0x49/0xb0
[ 98.823663] [<ffffffff81646f97>] system_call_fastpath+0x12/0x6f
[ 98.823663] Code: 48 83 ec 08 48 85 d2 0f 84 8e 00 00 00 48 85 ff 49 89 fd 0f 84 82 00 00 00 48 89 f3 48 c7 c7 a0 2c c8 81 41 89 ce e8 f0 89 3d 00 <48> 8b 1b 48 85 db 74 48 48 89 df e8 c0 bf ff ff 48 c7 c7 a0 2c
[ 98.823663] RIP [<ffffffff8126da50>] sysfs_do_create_link_sd.isra.2+0x40/0xd0
[ 98.823663] RSP <ffff88005d40fc28>
[ 98.823663] CR2: 0000000000000040
[ 98.823663] ---[ end trace e1035d8c51ec986e ]---
[ 98.823663] BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:21
[ 98.823663] in_atomic(): 1, irqs_disabled(): 1, pid: 2952, name: cat
[ 98.823663] INFO: lockdep is turned off.
[ 98.823663] irq event stamp: 3392
[ 98.823663] hardirqs last enabled at (3391): [<ffffffff81644133>] __mutex_unlock_slowpath+0xb3/0x180
[ 98.823663] hardirqs last disabled at (3392): [<ffffffff81648d33>] error_sti+0x5/0x6
[ 98.823663] softirqs last enabled at (0): [<ffffffff8105c6a9>] copy_process.part.35+0x4d9/0x1ce0
[ 98.823663] softirqs last disabled at (0): [< (null)>] (null)
[ 98.823663] CPU: 5 PID: 2952 Comm: cat Tainted: G D W 4.1.0-rc2-next-20150505+ #1260
[ 98.823663] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[ 98.823663] ffff88005d40f8c8 ffff88005d40f8c8 ffffffff8163d8d8 0000000000000000
[ 98.823663] 0000000000000000 ffff88005d40f8f8 ffffffff8108c18e ffffffff8108c005
[ 98.823663] ffffffff819ec8b3 0000000000000015 0000000000000000 ffff88005d40f928
[ 98.823663] Call Trace:
[ 98.823663] [<ffffffff8163d8d8>] dump_stack+0x4c/0x65
[ 98.823663] [<ffffffff8108c18e>] ___might_sleep+0x18e/0x250
[ 98.823663] [<ffffffff8108c005>] ? ___might_sleep+0x5/0x250
[ 98.823663] [<ffffffff8108c29d>] __might_sleep+0x4d/0x90
[ 98.823663] [<ffffffff8108c255>] ? __might_sleep+0x5/0x90
[ 98.823663] [<ffffffff81644494>] down_read+0x24/0x70
[ 98.823663] [<ffffffff81644475>] ? down_read+0x5/0x70
[ 98.823663] [<ffffffff810722a4>] ? exit_signals+0x24/0x130
[ 98.823663] [<ffffffff810722a4>] exit_signals+0x24/0x130
[ 98.823663] [<ffffffff81072285>] ? exit_signals+0x5/0x130
[ 98.823663] [<ffffffff810606f8>] ? do_exit+0xb8/0xbc0
[ 98.823663] [<ffffffff810606f8>] do_exit+0xb8/0xbc0
[ 98.823663] [<ffffffff81060645>] ? do_exit+0x5/0xbc0
[ 98.823663] [<ffffffff810c4a79>] ? kmsg_dump+0x119/0x1a0
[ 98.823663] [<ffffffff810c4985>] ? kmsg_dump+0x25/0x1a0
[ 98.823663] [<ffffffff8100665e>] oops_end+0x8e/0xd0
[ 98.823663] [<ffffffff810065d5>] ? oops_end+0x5/0xd0
[ 98.823663] [<ffffffff81637f65>] no_context+0x2d9/0x33e
[ 98.823663] [<ffffffff81637c91>] ? no_context+0x5/0x33e
[ 98.823663] [<ffffffff81638042>] __bad_area_nosemaphore+0x78/0x1d1
[ 98.823663] [<ffffffff816381a0>] ? bad_area_nosemaphore+0x5/0x15
[ 98.823663] [<ffffffff816381ae>] bad_area_nosemaphore+0x13/0x15
[ 98.823663] [<ffffffff8104c4de>] __do_page_fault+0x9e/0x490
[ 98.823663] [<ffffffff8104c445>] ? __do_page_fault+0x5/0x490
[ 98.823663] [<ffffffff8104c8dc>] do_page_fault+0xc/0x10
[ 98.823663] [<ffffffff81648b62>] page_fault+0x22/0x30
[ 98.823663] [<ffffffff8126da50>] ? sysfs_do_create_link_sd.isra.2+0x40/0xd0
[ 98.823663] [<ffffffff8126da50>] ? sysfs_do_create_link_sd.isra.2+0x40/0xd0
[ 98.823663] [<ffffffff8135931b>] ? disk_part_iter_next+0x2b/0x280
[ 98.823663] [<ffffffff8126db05>] sysfs_create_link+0x25/0x50
[ 98.823663] [<ffffffff81359fc2>] add_disk+0x252/0x4e0
[ 98.823663] [<ffffffff8137a9a4>] ? snprintf+0x34/0x40
[ 98.823663] [<ffffffff814867cc>] zram_add+0x1ec/0x2f0
[ 98.823663] [<ffffffff814868f2>] zram_add_show+0x22/0x60
[ 98.823663] [<ffffffff81469edb>] class_attr_show+0x1b/0x30
[ 98.823663] [<ffffffff8126d1ff>] sysfs_kf_seq_show+0xcf/0x1d0
[ 98.823663] [<ffffffff8126b716>] kernfs_seq_show+0x26/0x30
[ 98.823663] [<ffffffff8120eaf5>] seq_read+0xf5/0x3a0
[ 98.823663] [<ffffffff8126c040>] ? kernfs_vma_page_mkwrite+0xa0/0xa0
[ 98.823663] [<ffffffff8126c165>] kernfs_fop_read+0x125/0x180
[ 98.823663] [<ffffffff811e5c98>] __vfs_read+0x28/0xe0
[ 98.823663] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.823663] [<ffffffff811e5c75>] ? __vfs_read+0x5/0xe0
[ 98.823663] [<ffffffff811e62e6>] vfs_read+0x86/0x140
[ 98.823663] [<ffffffff81207fa7>] ? __fdget_pos+0x17/0x50
[ 98.823663] [<ffffffff811e7179>] SyS_read+0x49/0xb0
[ 98.823663] [<ffffffff81646f97>] system_call_fastpath+0x12/0x6f
[ 98.823663] note: cat[2952] exited with preempt_count 1

On Mon, May 04, 2015 at 03:57:13PM -0700, akpm@xxxxxxxxxxxxxxxxxxxx wrote:
>
> The patch titled
> Subject: zram: add dynamic device add/remove functionality
> has been added to the -mm tree. Its filename is
> zram-add-dynamic-device-add-remove-functionality.patch
>
> This patch should soon appear at
> http://ozlabs.org/~akpm/mmots/broken-out/zram-add-dynamic-device-add-remove-functionality.patch
> and later at
> http://ozlabs.org/~akpm/mmotm/broken-out/zram-add-dynamic-device-add-remove-functionality.patch
>
> Before you just go and hit "reply", please:
> a) Consider who else should be cc'ed
> b) Prefer to cc a suitable mailing list as well
> c) Ideally: find the original patch on the mailing list and do a
> reply-to-all to that, adding suitable additional cc's
>
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
>
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
>
> ------------------------------------------------------
> From: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Subject: zram: add dynamic device add/remove functionality
>
> We currently don't support on-demand device creation. The one and only
> way to have N zram devices is to specify num_devices module parameter
> (default value: 1). IOW if, for some reason, at some point, user wants to
> have N + 1 devies he/she must umount all the existing devices, unload the
> module, load the module passing num_devices equals to N + 1. And do this
> again, if needed.
>
> This patch introduces zram control sysfs class, which has two sysfs
> attrs:
> - zram_add -- add a new zram device
> - zram_remove -- remove a specific (device_id) zram device
>
> zram_add sysfs attr is read-only and has only automatic device id
> assignment mode (as requested by Minchan Kim). read operation performed
> on this attr creates a new zram device and returns back its device_id or
> error status.
>
> Usage example:
> # add a new specific zram device
> cat /sys/class/zram-control/zram_add
> 2
>
> # remove a specific zram device
> echo 4 > /sys/class/zram-control/zram_remove
>
> Returning zram_add() error code back to user (-ENOMEM in this case)
>
> cat /sys/class/zram-control/zram_add
> cat: /sys/class/zram-control/zram_add: Cannot allocate memory
>
> NOTE, there might be users who already depend on the fact that at least
> zram0 device gets always created by zram_init(). Preserve this behavior.
>
> [minchan@xxxxxxxxxx: use zram->claim to avoid lockdep splat]
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> Documentation/ABI/testing/sysfs-class-zram | 24 ++++
> Documentation/blockdev/zram.txt | 23 +++-
> drivers/block/zram/zram_drv.c | 100 ++++++++++++++++++-
> 3 files changed, 141 insertions(+), 6 deletions(-)
>
> diff -puN /dev/null Documentation/ABI/testing/sysfs-class-zram
> --- /dev/null
> +++ a/Documentation/ABI/testing/sysfs-class-zram
> @@ -0,0 +1,24 @@
> +What: /sys/class/zram-control/
> +Date: August 2015
> +KernelVersion: 4.2
> +Contact: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> +Description:
> + The zram-control/ class sub-directory belongs to zram
> + device class
> +
> +What: /sys/class/zram-control/zram_add
> +Date: August 2015
> +KernelVersion: 4.2
> +Contact: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> +Description:
> + RO attribute. Read operation will cause zram to add a new
> + device and return its device id back to user (so one can
> + use /dev/zram<id>), or error code.
> +
> +What: /sys/class/zram-control/zram_add
> +Date: August 2015
> +KernelVersion: 4.2
> +Contact: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> +Description:
> + Remove a specific /dev/zramX device, where X is a device_id
> + provided by user
> diff -puN Documentation/blockdev/zram.txt~zram-add-dynamic-device-add-remove-functionality Documentation/blockdev/zram.txt
> --- a/Documentation/blockdev/zram.txt~zram-add-dynamic-device-add-remove-functionality
> +++ a/Documentation/blockdev/zram.txt
> @@ -99,7 +99,24 @@ size of the disk when not in use so a hu
> mkfs.ext4 /dev/zram1
> mount /dev/zram1 /tmp
>
> -7) Stats:
> +7) Add/remove zram devices
> +
> +zram provides a control interface, which enables dynamic (on-demand) device
> +addition and removal.
> +
> +In order to add a new /dev/zramX device, perform read operation on zram_add
> +attribute. This will return either new device's device id (meaning that you
> +can use /dev/zram<id>) or error code.
> +
> +Example:
> + cat /sys/class/zram-control/zram_add
> + 1
> +
> +To remove the existing /dev/zramX device (where X is a device id)
> +execute
> + echo X > /sys/class/zram-control/zram_remove
> +
> +8) Stats:
> Per-device statistics are exported as various nodes under /sys/block/zram<id>/
>
> A brief description of exported device attritbutes. For more details please
> @@ -174,11 +191,11 @@ line of text and contains the following
> zero_pages
> num_migrated
>
> -8) Deactivate:
> +9) Deactivate:
> swapoff /dev/zram0
> umount /dev/zram1
>
> -9) Reset:
> +10) Reset:
> Write any positive value to 'reset' sysfs node
> echo 1 > /sys/block/zram0/reset
> echo 1 > /sys/block/zram1/reset
> diff -puN drivers/block/zram/zram_drv.c~zram-add-dynamic-device-add-remove-functionality drivers/block/zram/zram_drv.c
> --- a/drivers/block/zram/zram_drv.c~zram-add-dynamic-device-add-remove-functionality
> +++ a/drivers/block/zram/zram_drv.c
> @@ -29,10 +29,14 @@
> #include <linux/vmalloc.h>
> #include <linux/err.h>
> #include <linux/idr.h>
> +#include <linux/sysfs.h>
>
> #include "zram_drv.h"
>
> static DEFINE_IDR(zram_index_idr);
> +/* idr index must be protected */
> +static DEFINE_MUTEX(zram_index_mutex);
> +
> static int zram_major;
> static const char *default_compressor = "lzo";
>
> @@ -1271,24 +1275,104 @@ out_free_dev:
> return ret;
> }
>
> -static void zram_remove(struct zram *zram)
> +static int zram_remove(struct zram *zram)
> {
> - pr_info("Removed device: %s\n", zram->disk->disk_name);
> + struct block_device *bdev;
> +
> + bdev = bdget_disk(zram->disk, 0);
> + if (!bdev)
> + return -ENOMEM;
> +
> + mutex_lock(&bdev->bd_mutex);
> + if (bdev->bd_openers || zram->claim) {
> + mutex_unlock(&bdev->bd_mutex);
> + bdput(bdev);
> + return -EBUSY;
> + }
> +
> + zram->claim = true;
> + mutex_unlock(&bdev->bd_mutex);
> +
> /*
> * Remove sysfs first, so no one will perform a disksize
> - * store while we destroy the devices
> + * store while we destroy the devices. This also helps during
> + * zram_remove() -- zram_reset_device() is the last holder of
> + * ->init_lock, no later/concurrent disksize_store() or any
> + * other sysfs handlers are possible.
> */
> sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
> &zram_disk_attr_group);
>
> + /* Make sure all the pending I/O are finished */
> + fsync_bdev(bdev);
> zram_reset_device(zram);
> + bdput(bdev);
> +
> + pr_info("Removed device: %s\n", zram->disk->disk_name);
> +
> idr_remove(&zram_index_idr, zram->disk->first_minor);
> blk_cleanup_queue(zram->disk->queue);
> del_gendisk(zram->disk);
> put_disk(zram->disk);
> kfree(zram);
> + return 0;
> +}
> +
> +/* zram module control sysfs attributes */
> +static ssize_t zram_add_show(struct class *class,
> + struct class_attribute *attr,
> + char *buf)
> +{
> + int ret;
> +
> + mutex_lock(&zram_index_mutex);
> + ret = zram_add();
> + mutex_unlock(&zram_index_mutex);
> +
> + if (ret < 0)
> + return ret;
> + return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
> +}
> +
> +static ssize_t zram_remove_store(struct class *class,
> + struct class_attribute *attr,
> + const char *buf,
> + size_t count)
> +{
> + struct zram *zram;
> + int ret, dev_id;
> +
> + /* dev_id is gendisk->first_minor, which is `int' */
> + ret = kstrtoint(buf, 10, &dev_id);
> + if (ret)
> + return ret;
> + if (dev_id < 0)
> + return -EINVAL;
> +
> + mutex_lock(&zram_index_mutex);
> +
> + zram = idr_find(&zram_index_idr, dev_id);
> + if (zram)
> + ret = zram_remove(zram);
> + else
> + ret = -ENODEV;
> +
> + mutex_unlock(&zram_index_mutex);
> + return ret ? ret : count;
> }
>
> +static struct class_attribute zram_control_class_attrs[] = {
> + __ATTR_RO(zram_add),
> + __ATTR_WO(zram_remove),
> + __ATTR_NULL,
> +};
> +
> +static struct class zram_control_class = {
> + .name = "zram-control",
> + .owner = THIS_MODULE,
> + .class_attrs = zram_control_class_attrs,
> +};
> +
> static int zram_remove_cb(int id, void *ptr, void *data)
> {
> zram_remove(ptr);
> @@ -1297,6 +1381,7 @@ static int zram_remove_cb(int id, void *
>
> static void destroy_devices(void)
> {
> + class_unregister(&zram_control_class);
> idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
> idr_destroy(&zram_index_idr);
> unregister_blkdev(zram_major, "zram");
> @@ -1306,14 +1391,23 @@ static int __init zram_init(void)
> {
> int ret;
>
> + ret = class_register(&zram_control_class);
> + if (ret) {
> + pr_warn("Unable to register zram-control class\n");
> + return ret;
> + }
> +
> zram_major = register_blkdev(0, "zram");
> if (zram_major <= 0) {
> pr_warn("Unable to get major number\n");
> + class_unregister(&zram_control_class);
> return -EBUSY;
> }
>
> while (num_devices != 0) {
> + mutex_lock(&zram_index_mutex);
> ret = zram_add();
> + mutex_unlock(&zram_index_mutex);
> if (ret < 0)
> goto out_error;
> num_devices--;
> _
>
> Patches currently in -mm which might be from sergey.senozhatsky@xxxxxxxxx are
>
> revert-zram-move-compact_store-to-sysfs-functions-area.patch
> zram-add-compact-sysfs-entry-to-documentation.patch
> zram-cosmetic-zram_attr_ro-code-formatting-tweak.patch
> zram-use-idr-instead-of-zram_devices-array.patch
> zram-reorganize-code-layout.patch
> zram-remove-max_num_devices-limitation.patch
> zram-report-every-added-and-removed-device.patch
> zram-trivial-correct-flag-operations-comment.patch
> zram-return-zram-device_id-from-zram_add.patch
> zram-close-race-by-open-overriding.patch
> zram-add-dynamic-device-add-remove-functionality.patch
>

--
Kind regards,
Minchan Kim

Attachment: dynamic_remove.sh
Description: Bourne shell script