Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
On Friday 16 September 2016 05:40 PM, Al Viro wrote: > On Fri, Sep 16, 2016 at 01:19:19PM +0530, Vaishali Thakkar wrote: > >> Hi, >> >> Just a question regarding this change. As after this change >> dput() is sleepable, is it still safe to use if under the >> spinlock in the function d_prune_aliases? > > It has always been sleepable and it wouldn't have been safe to use > under spinlocks. Which d_prune_aliases() does not do - __dentry_kill() > is called with dentry, its parent and its inode (if present) all locked and > it drops all those locks before returning. Ah, I see. Alright. Thanks for the clarification. > -- Vaishali
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
On Friday 16 September 2016 05:40 PM, Al Viro wrote: > On Fri, Sep 16, 2016 at 01:19:19PM +0530, Vaishali Thakkar wrote: > >> Hi, >> >> Just a question regarding this change. As after this change >> dput() is sleepable, is it still safe to use if under the >> spinlock in the function d_prune_aliases? > > It has always been sleepable and it wouldn't have been safe to use > under spinlocks. Which d_prune_aliases() does not do - __dentry_kill() > is called with dentry, its parent and its inode (if present) all locked and > it drops all those locks before returning. Ah, I see. Alright. Thanks for the clarification. > -- Vaishali
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
On Fri, Sep 16, 2016 at 01:19:19PM +0530, Vaishali Thakkar wrote: > Hi, > > Just a question regarding this change. As after this change > dput() is sleepable, is it still safe to use if under the > spinlock in the function d_prune_aliases? It has always been sleepable and it wouldn't have been safe to use under spinlocks. Which d_prune_aliases() does not do - __dentry_kill() is called with dentry, its parent and its inode (if present) all locked and it drops all those locks before returning.
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
On Fri, Sep 16, 2016 at 01:19:19PM +0530, Vaishali Thakkar wrote: > Hi, > > Just a question regarding this change. As after this change > dput() is sleepable, is it still safe to use if under the > spinlock in the function d_prune_aliases? It has always been sleepable and it wouldn't have been safe to use under spinlocks. Which d_prune_aliases() does not do - __dentry_kill() is called with dentry, its parent and its inode (if present) all locked and it drops all those locks before returning.
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
On Wednesday 22 June 2016 08:31 AM, Wei Fang wrote: > We triggered soft-lockup under stress test which > open/access/write/close one file concurrently on more than > five different CPUs: > > WARN: soft lockup - CPU#0 stuck for 11s! [who:30631] > ... > [] dput+0x100/0x298 > [] terminate_walk+0x4c/0x60 > [] path_lookupat+0x5cc/0x7a8 > [] filename_lookup+0x38/0xf0 > [] user_path_at_empty+0x78/0xd0 > [] user_path_at+0x1c/0x28 > [] SyS_faccessat+0xb4/0x230 > > ->d_lock trylock may failed many times because of concurrently > operations, and dput() may execute a long time. > > Fix this by replacing cpu_relax() with cond_resched(). > dput() used to be sleepable, so make it sleepable again > should be safe. Hi, Just a question regarding this change. As after this change dput() is sleepable, is it still safe to use if under the spinlock in the function d_prune_aliases? Thanks > Cc:> Signed-off-by: Wei Fang > --- > Changes v1->v2: > - add might_sleep() to annotate that dput() can sleep > > fs/dcache.c |4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index d5ecc6e..074fc1c 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) > > failed: > spin_unlock(>d_lock); > - cpu_relax(); > + cond_resched(); > return dentry; /* try again with same dentry */ > } > > @@ -752,6 +752,8 @@ void dput(struct dentry *dentry) > return; > > repeat: > + might_sleep(); > + > rcu_read_lock(); > if (likely(fast_dput(dentry))) { > rcu_read_unlock(); > -- Vaishali
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
On Wednesday 22 June 2016 08:31 AM, Wei Fang wrote: > We triggered soft-lockup under stress test which > open/access/write/close one file concurrently on more than > five different CPUs: > > WARN: soft lockup - CPU#0 stuck for 11s! [who:30631] > ... > [] dput+0x100/0x298 > [] terminate_walk+0x4c/0x60 > [] path_lookupat+0x5cc/0x7a8 > [] filename_lookup+0x38/0xf0 > [] user_path_at_empty+0x78/0xd0 > [] user_path_at+0x1c/0x28 > [] SyS_faccessat+0xb4/0x230 > > ->d_lock trylock may failed many times because of concurrently > operations, and dput() may execute a long time. > > Fix this by replacing cpu_relax() with cond_resched(). > dput() used to be sleepable, so make it sleepable again > should be safe. Hi, Just a question regarding this change. As after this change dput() is sleepable, is it still safe to use if under the spinlock in the function d_prune_aliases? Thanks > Cc: > Signed-off-by: Wei Fang > --- > Changes v1->v2: > - add might_sleep() to annotate that dput() can sleep > > fs/dcache.c |4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index d5ecc6e..074fc1c 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) > > failed: > spin_unlock(>d_lock); > - cpu_relax(); > + cond_resched(); > return dentry; /* try again with same dentry */ > } > > @@ -752,6 +752,8 @@ void dput(struct dentry *dentry) > return; > > repeat: > + might_sleep(); > + > rcu_read_lock(); > if (likely(fast_dput(dentry))) { > rcu_read_unlock(); > -- Vaishali
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
Hi, Boqun, >> diff --git a/fs/dcache.c b/fs/dcache.c >> index d5ecc6e..074fc1c 100644 >> --- a/fs/dcache.c >> +++ b/fs/dcache.c >> @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) >> >> failed: >> spin_unlock(>d_lock); >> -cpu_relax(); >> +cond_resched(); > > Is it better to put the cond_resched() in the caller(i.e. dput()), right > before "goto repeat"? Because it's obviously a loop there, which makes > the purpose of cond_resched() more straightforward. Agreed, that's more reasonable. I'll send v3 soon. Thanks, Wei
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
Hi, Boqun, >> diff --git a/fs/dcache.c b/fs/dcache.c >> index d5ecc6e..074fc1c 100644 >> --- a/fs/dcache.c >> +++ b/fs/dcache.c >> @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) >> >> failed: >> spin_unlock(>d_lock); >> -cpu_relax(); >> +cond_resched(); > > Is it better to put the cond_resched() in the caller(i.e. dput()), right > before "goto repeat"? Because it's obviously a loop there, which makes > the purpose of cond_resched() more straightforward. Agreed, that's more reasonable. I'll send v3 soon. Thanks, Wei
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
Hi Wei Fang, On Wed, Jun 22, 2016 at 11:01:15AM +0800, Wei Fang wrote: > We triggered soft-lockup under stress test which > open/access/write/close one file concurrently on more than > five different CPUs: > > WARN: soft lockup - CPU#0 stuck for 11s! [who:30631] > ... > [] dput+0x100/0x298 > [] terminate_walk+0x4c/0x60 > [] path_lookupat+0x5cc/0x7a8 > [] filename_lookup+0x38/0xf0 > [] user_path_at_empty+0x78/0xd0 > [] user_path_at+0x1c/0x28 > [] SyS_faccessat+0xb4/0x230 > > ->d_lock trylock may failed many times because of concurrently > operations, and dput() may execute a long time. > > Fix this by replacing cpu_relax() with cond_resched(). > dput() used to be sleepable, so make it sleepable again > should be safe. > > Cc:> Signed-off-by: Wei Fang > --- > Changes v1->v2: > - add might_sleep() to annotate that dput() can sleep > > fs/dcache.c |4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index d5ecc6e..074fc1c 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) > > failed: > spin_unlock(>d_lock); > - cpu_relax(); > + cond_resched(); Is it better to put the cond_resched() in the caller(i.e. dput()), right before "goto repeat"? Because it's obviously a loop there, which makes the purpose of cond_resched() more straightforward. Regards, Boqun > return dentry; /* try again with same dentry */ > } > > @@ -752,6 +752,8 @@ void dput(struct dentry *dentry) > return; > > repeat: > + might_sleep(); > + > rcu_read_lock(); > if (likely(fast_dput(dentry))) { > rcu_read_unlock(); > -- > 1.7.1 > signature.asc Description: PGP signature
Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput()
Hi Wei Fang, On Wed, Jun 22, 2016 at 11:01:15AM +0800, Wei Fang wrote: > We triggered soft-lockup under stress test which > open/access/write/close one file concurrently on more than > five different CPUs: > > WARN: soft lockup - CPU#0 stuck for 11s! [who:30631] > ... > [] dput+0x100/0x298 > [] terminate_walk+0x4c/0x60 > [] path_lookupat+0x5cc/0x7a8 > [] filename_lookup+0x38/0xf0 > [] user_path_at_empty+0x78/0xd0 > [] user_path_at+0x1c/0x28 > [] SyS_faccessat+0xb4/0x230 > > ->d_lock trylock may failed many times because of concurrently > operations, and dput() may execute a long time. > > Fix this by replacing cpu_relax() with cond_resched(). > dput() used to be sleepable, so make it sleepable again > should be safe. > > Cc: > Signed-off-by: Wei Fang > --- > Changes v1->v2: > - add might_sleep() to annotate that dput() can sleep > > fs/dcache.c |4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index d5ecc6e..074fc1c 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) > > failed: > spin_unlock(>d_lock); > - cpu_relax(); > + cond_resched(); Is it better to put the cond_resched() in the caller(i.e. dput()), right before "goto repeat"? Because it's obviously a loop there, which makes the purpose of cond_resched() more straightforward. Regards, Boqun > return dentry; /* try again with same dentry */ > } > > @@ -752,6 +752,8 @@ void dput(struct dentry *dentry) > return; > > repeat: > + might_sleep(); > + > rcu_read_lock(); > if (likely(fast_dput(dentry))) { > rcu_read_unlock(); > -- > 1.7.1 > signature.asc Description: PGP signature