Kevin, Thanks for reviewing the patch. Chunqiu and I revised the patch. Pls see the attachment. Thanks, Limei,chunqiu -----Original Message----- From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] Sent: Thursday, August 13, 2009 8:02 AM To: Wang Limei-E12499 Cc: Romit Dasgupta; linux-omap@xxxxxxxxxxxxxxx; Wang Sawsd-A24013 Subject: Re: Linux-omap PM: Fix dead lock condition in resource_release(vdd1_opp) "Wang Limei-E12499" <E12499@xxxxxxxxxxxx> writes: > > Kevin and Romit, > > I agreed with you, thanks Kevin and Romit for the comments! Chunqiu > Wang coded resource-based mutex, below is the patch. Pls review and > let us know your feedback. > > > From 31f87ffb8eb1f854a9adb7fd96011d490f4655fa Mon Sep 17 00:00:00 2001 > From: Chunqiu Wang <cqwang@xxxxxxxxxxxx> > Date: Wed, 12 Aug 2009 16:22:09 +0800 > Subject: [PATCH] Fix resource framework mutex lock issue when > resource_get or resource_release are called nestedly. > Could use a shorter summary (subject) and a more detailed changelog. This patch is doing too many things in a single patch without enough explanation. Not only does it convert the global semaphore to a resource-specific semaphore, but it also changing the locking slightly by moving some things in/out of lock protection. That should be described in the changelog as well. Even better would be a first patch that simply converts the semaphore to a resource-specific *mutex* (not resource-specific semaphore.) IOW, use mutex API in <linux/mutex.h>: struct mutex; init_mutex() mutex_lock() mutex_unlock() mutex_is_lockec() ... Then, add a 2nd patch which does any reworking of the critical sections. Kevin > Signed-off-by: Chunqiu Wang <cqwang@xxxxxxxxxxxx> > --- > arch/arm/plat-omap/include/mach/resource.h | 2 + > arch/arm/plat-omap/resource.c | 38 > +++++++++++++-------------- > 2 files changed, 20 insertions(+), 20 deletions(-) > > diff --git a/arch/arm/plat-omap/include/mach/resource.h > b/arch/arm/plat-omap/include/mach/resource.h > index f91d8ce..389cb67 100644 > --- a/arch/arm/plat-omap/include/mach/resource.h > +++ b/arch/arm/plat-omap/include/mach/resource.h > @@ -22,6 +22,7 @@ > > #include <linux/list.h> > #include <linux/mutex.h> > +#include <linux/semaphore.h> > #include <linux/device.h> > #include <mach/cpu.h> > > @@ -46,6 +47,7 @@ struct shared_resource { > /* Shared resource operations */ > struct shared_resource_ops *ops; > struct list_head node; > + struct semaphore resource_mutex; > }; > > struct shared_resource_ops { > diff --git a/arch/arm/plat-omap/resource.c > b/arch/arm/plat-omap/resource.c index ec31727..758a138 100644 > --- a/arch/arm/plat-omap/resource.c > +++ b/arch/arm/plat-omap/resource.c > @@ -264,6 +264,7 @@ int resource_register(struct shared_resource *resp) > return -EEXIST; > > INIT_LIST_HEAD(&resp->users_list); > + sema_init(&resp->resource_mutex, 1); > > down(&res_mutex); > /* Add the resource to the resource list */ @@ -326,14 +327,14 @@ > int resource_request(const char *name, struct device *dev, > struct users_list *user; > int found = 0, ret = 0; > > - down(&res_mutex); > - resp = _resource_lookup(name); > + resp = resource_lookup(name); > if (!resp) { > printk(KERN_ERR "resource_request: Invalid resource name\n"); > ret = -EINVAL; > - goto res_unlock; > + goto ret; > } > > + down(&resp->resource_mutex); > /* Call the resource specific validate function */ > if (resp->ops->validate_level) { > ret = resp->ops->validate_level(resp, level); @@ -361,16 +362,12 @@ > int resource_request(const char *name, struct device *dev, > } > user->level = level; > > + /* Recompute and set the current level for the resource */ > + ret = update_resource_level(resp); > res_unlock: > - up(&res_mutex); > - /* > - * Recompute and set the current level for the resource. > - * NOTE: update_resource level moved out of spin_lock, as it may > call > - * pm_qos_add_requirement, which does a kzmalloc. This won't be > allowed > - * in iterrupt context. The spin_lock still protects add/remove > users. > - */ > - if (!ret) > - ret = update_resource_level(resp); > + up(&resp->resource_mutex); > + > +ret: > return ret; > } > EXPORT_SYMBOL(resource_request); > @@ -393,14 +390,14 @@ int resource_release(const char *name, struct > device *dev) > struct users_list *user; > int found = 0, ret = 0; > > - down(&res_mutex); > - resp = _resource_lookup(name); > + resp = resource_lookup(name); > if (!resp) { > printk(KERN_ERR "resource_release: Invalid resource name\n"); > ret = -EINVAL; > - goto res_unlock; > + goto ret; > } > > + down(&resp->resource_mutex); > list_for_each_entry(user, &resp->users_list, node) { > if (user->dev == dev) { > found = 1; > @@ -421,7 +418,9 @@ int resource_release(const char *name, struct > device > *dev) > /* Recompute and set the current level for the resource */ > ret = update_resource_level(resp); > res_unlock: > - up(&res_mutex); > + up(&resp->resource_mutex); > + > +ret: > return ret; > } > EXPORT_SYMBOL(resource_release); > @@ -438,15 +437,14 @@ int resource_get_level(const char *name) > struct shared_resource *resp; > u32 ret; > > - down(&res_mutex); > - resp = _resource_lookup(name); > + resp = resource_lookup(name); > if (!resp) { > printk(KERN_ERR "resource_release: Invalid resource name\n"); > - up(&res_mutex); > return -EINVAL; > } > + down(&resp->resource_mutex); > ret = resp->curr_level; > - up(&res_mutex); > + up(&resp->resource_mutex); > return ret; > } > EXPORT_SYMBOL(resource_get_level); > -- > 1.5.4.3 > > > > > > -----Original Message----- > From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] > Sent: Monday, August 10, 2009 11:23 AM > To: Wang Limei-E12499 > Cc: linux-omap@xxxxxxxxxxxxxxx > Subject: Re: Linux-omap PM: Fix dead lock condition in > resource_release(vdd1_opp) > > "Wang Limei-E12499" <E12499@xxxxxxxxxxxx> writes: > >> I am using linux-omap pm-2.6.29 >> <http://git.kernel.org/?p=linux/kernel/git/khilman/linux-omap-pm.git; >> a =s hortlog;h=pm-2.6.29> branch,found a dead lock condition in: >> arch/arm/plat-omap/resource.c->resource_release(). >> >> The dead lock happens when using >> resource_request("vdd1_opp",&dev,...) >> and resource_release("vdd1_opp", &dev) to set and release vdd1 opp >> constraint. The scenario is: >> >> plat-omap/resource.c/resource_release("vdd1_opp", >> &dev)==>resource.c/update_resource_level()=>mach-omap2/resource34xx.c >> / se t_opp(). In set_opp(), if the target_level of vdd1 is less >> than OPP3,will release the constraint set on VDD2 by calling >> resource_release(), but it will never return because can not get the >> mutex which is holding by the previous caller. >> >> int resource_release(const char *name, struct device *dev) >> { ....... >> down(&res_mutex); >> ........ >> /* Recompute and set the current level for the resource */ >> ret = update_resource_level(resp); >> res_unlock: >> up(&res_mutex); >> return ret; >> } >> >> int set_opp(struct shared_resource *resp, u32 target_level) { >> ..... >> if (resp == vdd1_resp) { >> if (target_level < 3) >> resource_release("vdd2_opp", &vdd2_dev); } >> >> The patch to fix this issue is below, will you pls review it and let >> me know your feedback? >> >> From: Limei Wang <e12499@xxxxxxxxxxxx> >> Date: Fri, 7 Aug 2009 11:40:35 -0500 >> Subject: [PATCH] OMAP PM: Fix dead lock bug in >> resourc_release(vdd1_opp). >> >> >> Signed-off-by: Limei Wang <e12499@xxxxxxxxxxxx> >> --- >> arch/arm/plat-omap/resource.c | 6 ++++-- >> 1 files changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm/plat-omap/resource.c >> b/arch/arm/plat-omap/resource.c index ec31727..876fd12 100644 >> --- a/arch/arm/plat-omap/resource.c >> +++ b/arch/arm/plat-omap/resource.c >> @@ -418,10 +418,12 @@ int resource_release(const char *name, struct >> device *dev) >> list_del(&user->node); >> free_user(user); >> >> - /* Recompute and set the current level for the resource */ >> - ret = update_resource_level(resp); >> res_unlock: >> up(&res_mutex); >> + >> + /* Recompute and set the current level for the resource */ >> + if (!ret) >> + ret = update_resource_level(resp); >> return ret; >> } >> EXPORT_SYMBOL(resource_release); >> -- >> 1.5.6.3 > > This is wrong for several reasons. > > First, you're not fixing the problem, you're just moving the call > outside of the lock, thus creating other locking problems. > > Second, the various error paths would break because > update_resource_level() would be called on the 'res_unlock' error path > where it is not currently being called. > > A per-resource mutex as suggest by Romit seems like the right approach > to fixing this problem. > > Kevin
Attachment:
0002-Move-the-resource-level-update-into-mutex_lock-block.patch
Description: 0002-Move-the-resource-level-update-into-mutex_lock-block.patch
Attachment:
0001-Add-per-resource-mutex-for-OMAP-resource-framework.patch
Description: 0001-Add-per-resource-mutex-for-OMAP-resource-framework.patch
