| Message ID | 20120424153046.GB1474@quack.suse.cz |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On 04/24/2012 11:30 PM, Jan Kara wrote: > Hello, > > On Tue 24-04-12 14:25:44, Jeff Liu wrote: >> I just ran into an issue on vanilla-kernel-3.3.0 when executing quotaon(8) on ext4 with "usrquota,grpquota", and there >> have files are being writing at the same time. >> >> I have a lxc guest running on an ext4 partition, >> $ mount|grep sda6 >> /dev/sda6 on /ext4 type ext4 (rw,usrquota,grpquota) >> >> Execute quotacheck -cvumg /ext4 to force the quota checking without shutdown that guest, at this stage, everything is fine, >> # quotacheck -cvgum /ext4 >> quotacheck: Your kernel probably supports journaled quota but you are not using it. Consider switching to journaled quota to avoid running quotacheck after an unclean shutdown. >> quotacheck: Scanning /dev/sda6 [/ext4] done >> quotacheck: Cannot stat old user quota file /ext4/aquota.user: No such file or directory. Usage will not be subtracted. >> quotacheck: Cannot stat old group quota file /ext4/aquota.group: No such file or directory. Usage will not be subtracted. >> quotacheck: Cannot stat old user quota file /ext4/aquota.user: No such file or directory. Usage will not be subtracted. >> quotacheck: Cannot stat old group quota file /ext4/aquota.group: No such file or directory. Usage will not be subtracted. >> quotacheck: Checked 3357 directories and 39335 files >> quotacheck: Old file not found. >> quotacheck: Old file not found. >> >> However, the kernel was hang when running quotaon /ext4. >> >> I observed the following info via netconsole: >> >> [ 423.140177] *** DEADLOCK *** >> [ 423.140177] >> [ 423.140177] May be due to missing lock nesting notation >> [ 423.140177] >> [ 423.140177] 4 locks held by quotaon/2350: >> [ 423.140177] #0: (&type->s_umount_key#26){++++++}, at: [<c122248e>] get_super+0xf9/0x1ec >> [ 423.140177] #1: (&s->s_dquot.dqonoff_mutex){+.+...}, at: [<c129b736>] vfs_load_quota_inode+0x3e5/0xac6 >> [ 423.140177] #2: (inode_sb_list_lock){+.+...}, at: [<c129b99b>] vfs_load_quota_inode+0x64a/0xac6 >> [ 423.140177] #3: (&sb->s_type->i_lock_key#16){+.+...}, at: [<c129b9de>] vfs_load_quota_inode+0x68d/0xac6 >> [ 423.140177] >> [ 423.140177] stack backtrace: >> [ 423.140177] Pid: 2350, comm: quotaon Not tainted 3.3.0 #79 >> [ 423.140177] Call Trace: >> [ 423.140177] [<c182b385>] ? printk+0x57/0x6a >> [ 423.140177] [<c10ee73e>] __lock_acquire+0x133d/0x1a8a >> [ 423.140177] [<c105da85>] ? vprintk+0x910/0x93a >> [ 423.140177] [<c1298068>] ? inode_get_rsv_space+0x45/0x8b >> [ 423.140177] [<c10ef795>] lock_acquire+0x13a/0x176 >> [ 423.140177] [<c1298068>] ? inode_get_rsv_space+0x45/0x8b >> [ 423.140177] [<c182f778>] _raw_spin_lock+0x54/0x7d >> [ 423.140177] [<c1298068>] ? inode_get_rsv_space+0x45/0x8b >> [ 423.140177] [<c1298068>] inode_get_rsv_space+0x45/0x8b >> [ 423.140177] [<c129bbe2>] vfs_load_quota_inode+0x891/0xac6 >> [ 423.140177] [<c129c1cb>] dquot_quota_on+0x82/0x97 >> [ 423.140177] [<f825d352>] ext4_quota_on+0x191/0x219 [ext4] >> [ 423.140177] [<c106e4e5>] ? ns_capable+0x71/0xa3 >> [ 423.140177] [<c129e300>] do_quotactl+0x2f7/0x80f >> [ 423.140177] [<f825d1c1>] ? ext4_msg+0x61/0x61 [ext4] >> [ 423.140177] [<c122248e>] ? get_super+0xf9/0x1ec >> [ 423.140177] [<c1222788>] ? get_super_thawed+0x33/0x147 >> [ 423.140177] [<c1246311>] ? iput+0x66/0x320 >> [ 423.140177] [<c129eaa8>] sys_quotactl+0x290/0x2fc >> [ 423.140177] [<c18308ec>] syscall_call+0x7/0xb >> >> As per my investigation, it occurred due to inode_get_rsv_space(inode) lock acquiring if the kernel was built with QUOTA_DEBUG enabled. >> At add_dquot_ref(), the lock did not released if the inode.i_writecount is not *ZERO*, inode is not in I_FREEING|I_WILL_FREE|I_NEW state, >> as well as it need to do quota init. >> >> if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) || >> !atomic_read(&inode->i_writecount) || >> !dqinit_needed(inode, type)) { >> spin_unlock(&inode->i_lock); >> continue; >> } >> >> #ifdef CONFIG_QUOTA_DEBUG >> if (unlikely(inode_get_rsv_space(inode) > 0)) >> reserved = 1; >> #endif >> >> In my situation, atomic_read(&inode->i_writecount) returns -2, looks that the related file have two >> deny-writers via mmap at that time. >> >> To nail down this issue, I refresh formated an ext4 file system, and try to open a file and keep writing to it(so that the atomic_read(&inode->i_writecount) = 1). >> then perform quotacheck and quotaon at the same time, and repeat this process for 4 times, the kernel hang for 3 times, 1 time its ok. >> >> # python -c "f=open('/ext4/test', 'w'); [(f.seek(x) or f.write(str(x))) for x in range(1, 1000000000, 99)]; f.close()" >> # quotacheck -cvumg /ext4 >> quotacheck: Your kernel probably supports journaled quota but you are not using it. Consider switching to journaled quota to avoid running quotacheck after an unclean shutdown. >> quotacheck: Scanning /dev/sda6 [/ext4] done >> quotacheck: Cannot stat old user quota file /ext4/aquota.user: No such file or directory. Usage will not be subtracted. >> quotacheck: Cannot stat old group quota file /ext4/aquota.group: No such file or directory. Usage will not be subtracted. >> quotacheck: Cannot stat old user quota file /ext4/aquota.user: No such file or directory. Usage will not be subtracted. >> quotacheck: Cannot stat old group quota file /ext4/aquota.group: No such file or directory. Usage will not be subtracted. >> quotacheck: Checked 2 directories and 1 files >> quotacheck: Old file not found. >> quotacheck: Old file not found. >> # quotaon /ext4 /* kernel was hang. */ >> >> I also verified that this issue can be reproduced against the latest kernel commit(Mon Apr 23 19:52:00 2012 95f714727436836bb46236ce2bcd8ee8f9274aed). >> >> Below is a small patch, it looks a bit ugly, but works for me. > Thanks for the detailed analysis and the patch! You are correct that it > is wrong to call inode_get_rsv_space() with i_lock held. However we cannot > just drop it at that place of add_dquot_ref() because than inode could be > removed from memory before we call __iget(). The right fix is to move > inode_get_rsv_space() to a later place in the function where i_lock is no > longer held. Attached patch should fix the problem. Thanks for your quick response and confirmation! Regards, -Jeff > > Honza -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From 1c8eb28ff0f58eb571c5c2150c36aebbd86cc9d9 Mon Sep 17 00:00:00 2001 From: Jan Kara <jack@suse.cz> Date: Tue, 24 Apr 2012 17:08:41 +0200 Subject: [PATCH] quota: Fix double lock in add_dquot_ref() with CONFIG_QUOTA_DEBUG When CONFIG_QUOTA_DEBUG is enabled we call inode_get_rsv_space() from add_dquot_ref() while holding i_lock. But inode_get_rsv_space() is trying to get i_lock as well resulting in double lock. Fix the problem by moving inode_get_rsv_space() call out of i_lock. Reported-and-analyzed-by: Jie Liu <jeff.liu@oracle.com> Signed-off-by: Jan Kara <jack@suse.cz> --- fs/quota/dquot.c | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index d69a1d1..0dcdda3 100644 --- a/fs/quota/dquot.c +++ b/fs/quota/dquot.c @@ -907,14 +907,14 @@ static void add_dquot_ref(struct super_block *sb, int type) spin_unlock(&inode->i_lock); continue; } -#ifdef CONFIG_QUOTA_DEBUG - if (unlikely(inode_get_rsv_space(inode) > 0)) - reserved = 1; -#endif __iget(inode); spin_unlock(&inode->i_lock); spin_unlock(&inode_sb_list_lock); +#ifdef CONFIG_QUOTA_DEBUG + if (unlikely(inode_get_rsv_space(inode) > 0)) + reserved = 1; +#endif iput(old_inode); __dquot_initialize(inode, type); -- 1.7.1