| Message ID | 20190211125337.16099-3-chintan.pandya@oneplus.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Potential race condition with page lock | expand |
On Mon, Feb 11, 2019 at 12:53:55PM +0000, Chintan Pandya wrote: > Some of the page flags, like PG_locked is not supposed to > be set twice. Currently, there is no protection around this > and many callers directly tries to set this bit. Others > follow trylock_page() which is much safer version of the > same. But, for performance issues, we may not want to > implement wait-until-set. So, at least, find out who is > doing double setting and fix them. > > Change-Id: I1295fcb8527ce4b54d5d11c11287fc7516006cf0 > Signed-off-by: Chintan Pandya <chintan.pandya@oneplus.com> > --- > include/linux/page-flags.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index a56a9bd4bc6b..e307775c2b4a 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -208,7 +208,7 @@ static __always_inline int Page##uname(struct page *page) \ > > #define SETPAGEFLAG(uname, lname, policy) \ > static __always_inline void SetPage##uname(struct page *page) \ > - { set_bit(PG_##lname, &policy(page, 1)->flags); } > + { WARN_ON(test_and_set_bit(PG_##lname, &policy(page, 1)->flags)); } You forgot to make this depend on CONFIG_DEBUG_VM. Also, I'm not convinced this is always wrong, inefficient sure, but not wrong in general.
On 11/02/19 7:17 PM, Peter Zijlstra wrote: > On Mon, Feb 11, 2019 at 12:53:55PM +0000, Chintan Pandya wrote: >> Some of the page flags, like PG_locked is not supposed to >> be set twice. Currently, there is no protection around this >> and many callers directly tries to set this bit. Others >> follow trylock_page() which is much safer version of the >> same. But, for performance issues, we may not want to >> implement wait-until-set. So, at least, find out who is >> doing double setting and fix them. >> >> Change-Id: I1295fcb8527ce4b54d5d11c11287fc7516006cf0 >> Signed-off-by: Chintan Pandya <chintan.pandya@oneplus.com> >> --- >> include/linux/page-flags.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index a56a9bd4bc6b..e307775c2b4a 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h >> @@ -208,7 +208,7 @@ static __always_inline int Page##uname(struct page *page) \ >> >> #define SETPAGEFLAG(uname, lname, policy) \ >> static __always_inline void SetPage##uname(struct page *page) \ >> - { set_bit(PG_##lname, &policy(page, 1)->flags); } >> + { WARN_ON(test_and_set_bit(PG_##lname, &policy(page, 1)->flags)); } > > You forgot to make this depend on CONFIG_DEBUG_VM. Also, I'm not > convinced this is always wrong, inefficient sure, but not wrong in > general. Okay. Will protect this under CONFIG_DEBUG_VM.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index a56a9bd4bc6b..e307775c2b4a 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -208,7 +208,7 @@ static __always_inline int Page##uname(struct page *page) \ #define SETPAGEFLAG(uname, lname, policy) \ static __always_inline void SetPage##uname(struct page *page) \ - { set_bit(PG_##lname, &policy(page, 1)->flags); } + { WARN_ON(test_and_set_bit(PG_##lname, &policy(page, 1)->flags)); } #define CLEARPAGEFLAG(uname, lname, policy) \ static __always_inline void ClearPage##uname(struct page *page) \
Some of the page flags, like PG_locked is not supposed to be set twice. Currently, there is no protection around this and many callers directly tries to set this bit. Others follow trylock_page() which is much safer version of the same. But, for performance issues, we may not want to implement wait-until-set. So, at least, find out who is doing double setting and fix them. Change-Id: I1295fcb8527ce4b54d5d11c11287fc7516006cf0 Signed-off-by: Chintan Pandya <chintan.pandya@oneplus.com> --- include/linux/page-flags.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)