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Commit 1fa5efe3622db58cb8c7b9a50665e9eb9a6c7e97 (ext4: Use generic helpers for quotaon and quotaoff) made possible to call quotactl(Q_XQUOTAON/OFF) on ext4 filesystems with sysfile quota support. This leads to calling dquot_enable/disable without s_umount held in excl. mode, because quotactl_cmd_onoff checks only for Q_QUOTAON/OFF. The following WARN_ON_ONCE triggers (in this case for dquot_enable, ext4, latest Linus' tree): [ 117.807056] EXT4-fs (dm-0): mounted filesystem with ordered data mode. Opts: quota,prjquota [...] [ 155.036847] WARNING: CPU: 0 PID: 2343 at fs/quota/dquot.c:2469 dquot_enable+0x34/0xb9 [ 155.036851] Modules linked in: quota_v2 quota_tree ipv6 af_packet joydev mousedev psmouse serio_raw pcspkr i2c_piix4 intel_agp intel_gtt e1000 ttm drm_kms_helper drm agpgart fb_sys_fops syscopyarea sysfillrect sysimgblt i2c_core input_leds kvm_intel kvm irqbypass qemu_fw_cfg floppy evdev parport_pc parport button crc32c_generic dm_mod ata_generic pata_acpi ata_piix libata loop ext4 crc16 mbcache jbd2 usb_storage usbcore sd_mod scsi_mod [ 155.036901] CPU: 0 PID: 2343 Comm: qctl Not tainted 4.20.0-rc6-00025-gf5d582777bcb #9 [ 155.036903] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 [ 155.036911] RIP: 0010:dquot_enable+0x34/0xb9 [ 155.036915] Code: 41 56 41 55 41 54 55 53 4c 8b 6f 28 74 02 0f 0b 4d 8d 7d 70 49 89 fc 89 cb 41 89 d6 89 f5 4c 89 ff e8 23 09 ea ff 85 c0 74 0a <0f> 0b 4c 89 ff e8 8b 09 ea ff 85 db 74 6a 41 8b b5 f8 00 00 00 0f [ 155.036918] RSP: 0018:ffffb09b00493e08 EFLAGS: 00010202 [ 155.036922] RAX: 0000000000000001 RBX: 0000000000000008 RCX: 0000000000000008 [ 155.036924] RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff9781b67cd870 [ 155.036926] RBP: 0000000000000002 R08: 0000000000000000 R09: 61c8864680b583eb [ 155.036929] R10: ffffb09b00493e48 R11: ffffffffff7ce7d4 R12: ffff9781b7ee8d78 [ 155.036932] R13: ffff9781b67cd800 R14: 0000000000000004 R15: ffff9781b67cd870 [ 155.036936] FS: 00007fd813250b88(0000) GS:ffff9781ba000000(0000) knlGS:0000000000000000 [ 155.036939] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 155.036942] CR2: 00007fd812ff61d6 CR3: 000000007c882000 CR4: 00000000000006b0 [ 155.036951] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 155.036953] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 155.036955] Call Trace: [ 155.037004] dquot_quota_enable+0x8b/0xd0 [ 155.037011] kernel_quotactl+0x628/0x74e [ 155.037027] ? do_mprotect_pkey+0x2a6/0x2cd [ 155.037034] __x64_sys_quotactl+0x1a/0x1d [ 155.037041] do_syscall_64+0x55/0xe4 [ 155.037078] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 155.037105] RIP: 0033:0x7fd812fe1198 [ 155.037109] Code: 02 77 0d 48 89 c1 48 c1 e9 3f 75 04 48 8b 04 24 48 83 c4 50 5b c3 48 83 ec 08 49 89 ca 48 63 d2 48 63 ff b8 b3 00 00 00 0f 05 <48> 89 c7 e8 c1 eb ff ff 5a c3 48 63 ff b8 bb 00 00 00 0f 05 48 89 [ 155.037112] RSP: 002b:00007ffe8cd7b050 EFLAGS: 00000206 ORIG_RAX: 00000000000000b3 [ 155.037116] RAX: ffffffffffffffda RBX: 00007ffe8cd7b148 RCX: 00007fd812fe1198 [ 155.037119] RDX: 0000000000000000 RSI: 00007ffe8cd7cea9 RDI: 0000000000580102 [ 155.037121] RBP: 00007ffe8cd7b0f0 R08: 000055fc8eba8a9d R09: 0000000000000000 [ 155.037124] R10: 00007ffe8cd7b074 R11: 0000000000000206 R12: 00007ffe8cd7b168 [ 155.037126] R13: 000055fc8eba8897 R14: 0000000000000000 R15: 0000000000000000 [ 155.037131] ---[ end trace 210f864257175c51 ]--- and then the syscall proceeds without s_umount locking. This patch locks the superblock ->s_umount sem. in exclusive mode for all Q_XQUOTAON/OFF quotactls too in addition to Q_QUOTAON/OFF. AFAICT, other than ext4, only xfs and ocfs2 are affected by this change. The VFS will now call in xfs_quota_* functions with s_umount held, which wasn't the case before. This looks good to me but I can not say for sure. Ext4 and ocfs2 where already beeing called with s_umount exclusive via quota_quotaon/off which is basically the same. Signed-off-by: Javier Barrio <javier.barrio.mart@gmail.com> Signed-off-by: Jan Kara <jack@suse.cz>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.