Hi, On 11/09/2013 21:19, Kim Jaegeuk wrote: > Hi Russ, > > The usage of fs_locks is for the recovery, so it doesn't matter > with stress-testing. > Actually what I've concerned is that we should not grab two or > more fs_locks in the same call path. > Thanks, >
I am wondering why we don't use other kind of methods like r/w semaphore instead of the fs_locks for access control purpose. Is it due to the little lower performance of r/w semaphore or other reasons? I think the r/w semaphore can bring more clearer access control over the current fs_locks, and will not suffer the problems reported here. It can be used in a way that i/o tasks just acquire read sem while the checkpoint task takes the write sem. Or do we have other better method? Regards, Jin > 2013/9/11 Russ Knize <[email protected]>: >> Hi Jaegeuk/Gu, >> >> I've removed the lock and have been stress-testing with SELinux and some >> additional xattr torture for 24+ hours. I have not encountered any issues >> yet. >> >> My previous suggestion about moving the lock is probably not a good idea >> without some significant code rework (thanks to the f2fs_balance_fs call in >> f2fs_setxattr). >> >> Russ >> >> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng <[email protected]> wrote: >>> >>> Hi Jaegeuk, >>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote: >>> >>>> Hi, >>>> >>>> 2013-09-07 (토), 08:00 +0000, Chao Yu: >>>>> Hi Knize, >>>>> >>>>> Thanks for your reply, I think it's actually meaningless that it's >>>>> being named after "spin_lock", >>>>> it's better to rename this spinlock to "round_robin_lock". >>>>> >>>>> This patch can only resolve the issue of unbalanced fs_lock usage, >>>>> it can not fix the deadlock issue. >>>>> can we fix deadlock issue through this method: >>>>> >>>>> - vfs_create() >>>>> - f2fs_create() - takes an fs_lock and save current thread info into >>>>> thread_info[NR_GLOBAL_LOCKS] >>>>> - f2fs_add_link() >>>>> - __f2fs_add_link() >>>>> - init_inode_metadata() >>>>> - f2fs_init_security() >>>>> - security_inode_init_security() >>>>> - f2fs_initxattrs() >>>>> - f2fs_setxattr() - get fs_lock only if there is no current >>>>> thread info in thread_info >>>>> >>>>> So it keeps one thread can only hold one fs_lock to avoid deadlock. >>>>> Can we use this solution? >>>> >>>> It could be. >>>> But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs() >>> >>> Agree. This fs_lock here is used to protect the xattr from parallel >>> modification, >>> but here is in the initxattrs routine, parallel modification can not >>> happen. >>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used >>> to >>> avoid parallel modification. So I think this fs_lock is needless. >>> Am I missing something? >>> >>> Regards, >>> Gu >>> >>>> level, since this case only happens when f2fs_initxattrs() is called. >>>> Let's think about ut in more detail. >>>> Thanks, >>>> >>>>> >>>>> >>>>> >>>>> thanks again! >>>>> >>>>> >>>>> >>>>> ------- Original Message ------- >>>>> >>>>> Sender : Russ Knize<[email protected]> >>>>> >>>>> Date : 九月 07, 2013 04:25 (GMT+09:00) >>>>> >>>>> Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better >>>>> performance >>>>> >>>>> >>>>> >>>>> I encountered this same issue recently and solved it in much the same >>>>> way. Can we rename "spin_lock" to something more meaningful? >>>>> >>>>> >>>>> This race actually exposed a potential deadlock between f2fs_create() >>>>> and f2fs_initxattrs(): >>>>> >>>>> >>>>> - vfs_create() >>>>> - f2fs_create() - takes an fs_lock >>>>> - f2fs_add_link() >>>>> - __f2fs_add_link() >>>>> - init_inode_metadata() >>>>> - f2fs_init_security() >>>>> - security_inode_init_security() >>>>> - f2fs_initxattrs() >>>>> - f2fs_setxattr() - also takes an fs_lock >>>>> >>>>> >>>>> If another CPU happens to have the same lock that f2fs_setxattr() was >>>>> trying to take because of the race around next_lock_num, we can get >>>>> into a deadlock situation if the two threads are also contending over >>>>> another resource (like bdi). >>>>> >>>>> >>>>> Another scenario is if the above happens while another thread is in >>>>> the middle of grabbing all of the locks via mutex_lock_all(). >>>>> f2fs_create() is holding a lock that mutex_lock_all() is waiting for >>>>> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting >>>>> for. >>>>> >>>>> >>>>> Russ >>>>> >>>>> >>>>> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <[email protected]> wrote: >>>>> Hi Kim: >>>>> >>>>> I think there is a performance problem: when all >>>>> sbi->fs_lock is holded, >>>>> >>>>> then all other threads may get the same next_lock value from >>>>> sbi->next_lock_num in function mutex_lock_op, >>>>> >>>>> and wait to get the same lock at position fs_lock[next_lock], >>>>> it unbalance the fs_lock usage. >>>>> >>>>> It may lost performance when we do the multithread test. >>>>> >>>>> >>>>> >>>>> Here is the patch to fix this problem: >>>>> >>>>> >>>>> >>>>> Signed-off-by: Yu Chao <[email protected]> >>>>> >>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h >>>>> >>>>> old mode 100644 >>>>> >>>>> new mode 100755 >>>>> >>>>> index 467d42d..983bb45 >>>>> >>>>> --- a/fs/f2fs/f2fs.h >>>>> >>>>> +++ b/fs/f2fs/f2fs.h >>>>> >>>>> @@ -371,6 +371,7 @@ struct f2fs_sb_info { >>>>> >>>>> struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS >>>>> operations */ >>>>> >>>>> struct mutex node_write; /* locking >>>>> node writes */ >>>>> >>>>> struct mutex writepages; /* mutex for >>>>> writepages() */ >>>>> >>>>> + spinlock_t spin_lock; /* lock for >>>>> next_lock_num */ >>>>> >>>>> unsigned char next_lock_num; /* round-robin >>>>> global locks */ >>>>> >>>>> int por_doing; /* recovery is >>>>> doing or not */ >>>>> >>>>> int on_build_free_nids; /* >>>>> build_free_nids is doing */ >>>>> >>>>> @@ -533,15 +534,19 @@ static inline void >>>>> mutex_unlock_all(struct f2fs_sb_info *sbi) >>>>> >>>>> >>>>> >>>>> static inline int mutex_lock_op(struct f2fs_sb_info *sbi) >>>>> >>>>> { >>>>> >>>>> - unsigned char next_lock = sbi->next_lock_num % >>>>> NR_GLOBAL_LOCKS; >>>>> >>>>> + unsigned char next_lock; >>>>> >>>>> int i = 0; >>>>> >>>>> >>>>> >>>>> for (; i < NR_GLOBAL_LOCKS; i++) >>>>> >>>>> if (mutex_trylock(&sbi->fs_lock[i])) >>>>> >>>>> return i; >>>>> >>>>> >>>>> >>>>> - mutex_lock(&sbi->fs_lock[next_lock]); >>>>> >>>>> + spin_lock(&sbi->spin_lock); >>>>> >>>>> + next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS; >>>>> >>>>> sbi->next_lock_num++; >>>>> >>>>> + spin_unlock(&sbi->spin_lock); >>>>> >>>>> + >>>>> >>>>> + mutex_lock(&sbi->fs_lock[next_lock]); >>>>> >>>>> return next_lock; >>>>> >>>>> } >>>>> >>>>> >>>>> >>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c >>>>> >>>>> old mode 100644 >>>>> >>>>> new mode 100755 >>>>> >>>>> index 75c7dc3..4f27596 >>>>> >>>>> --- a/fs/f2fs/super.c >>>>> >>>>> +++ b/fs/f2fs/super.c >>>>> >>>>> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct >>>>> super_block *sb, void *data, int silent) >>>>> >>>>> mutex_init(&sbi->cp_mutex); >>>>> >>>>> for (i = 0; i < NR_GLOBAL_LOCKS; i++) >>>>> >>>>> mutex_init(&sbi->fs_lock[i]); >>>>> >>>>> + spin_lock_init(&sbi->spin_lock); >>>>> >>>>> mutex_init(&sbi->node_write); >>>>> >>>>> sbi->por_doing = 0; >>>>> >>>>> spin_lock_init(&sbi->stat_lock); >>>>> >>>>> (END) >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL >>>>> 2012, more! >>>>> Discover the easy way to master current and previous Microsoft >>>>> technologies >>>>> and advance your career. 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