| Message ID | 1466564475-30417-1-git-send-email-fangwei1@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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] > ... > [<ffffffc0003986f8>] dput+0x100/0x298 > [<ffffffc00038c2dc>] terminate_walk+0x4c/0x60 > [<ffffffc00038f56c>] path_lookupat+0x5cc/0x7a8 > [<ffffffc00038f780>] filename_lookup+0x38/0xf0 > [<ffffffc000391180>] user_path_at_empty+0x78/0xd0 > [<ffffffc0003911f4>] user_path_at+0x1c/0x28 > [<ffffffc00037d4fc>] 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: <stable@vger.kernel.org> > Signed-off-by: Wei Fang <fangwei1@huawei.com> > --- > 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(&dentry->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 >
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(&dentry->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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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] > ... > [<ffffffc0003986f8>] dput+0x100/0x298 > [<ffffffc00038c2dc>] terminate_walk+0x4c/0x60 > [<ffffffc00038f56c>] path_lookupat+0x5cc/0x7a8 > [<ffffffc00038f780>] filename_lookup+0x38/0xf0 > [<ffffffc000391180>] user_path_at_empty+0x78/0xd0 > [<ffffffc0003911f4>] user_path_at+0x1c/0x28 > [<ffffffc00037d4fc>] 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: <stable@vger.kernel.org> > Signed-off-by: Wei Fang <fangwei1@huawei.com> > --- > 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(&dentry->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(); >
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. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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. >
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(&dentry->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();
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] ... [<ffffffc0003986f8>] dput+0x100/0x298 [<ffffffc00038c2dc>] terminate_walk+0x4c/0x60 [<ffffffc00038f56c>] path_lookupat+0x5cc/0x7a8 [<ffffffc00038f780>] filename_lookup+0x38/0xf0 [<ffffffc000391180>] user_path_at_empty+0x78/0xd0 [<ffffffc0003911f4>] user_path_at+0x1c/0x28 [<ffffffc00037d4fc>] 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: <stable@vger.kernel.org> Signed-off-by: Wei Fang <fangwei1@huawei.com> --- Changes v1->v2: - add might_sleep() to annotate that dput() can sleep fs/dcache.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-)