| Message ID | 1403881067-22690-3-git-send-email-jean.pihet@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Jean, On Fri, Jun 27, 2014 at 03:57:46PM +0100, Jean Pihet wrote: > As done on other architectures (ARM64, x86, Sparc etc.). > > This prevents a deadlock on down_read in do_page_fault when unwinding > using fp and triggering on kernel tracepoints: So is this an issue because you could try setting tracepoints on the pagefault path? If so, the patch is a little brutal as it would break user backtracing as soon as we take any old page fault, no? Or am I missing something obvious? Will > INFO: task stress:2116 blocked for more than 120 seconds. > Not tainted 3.15.0-rc4-00364-g3401dfb-dirty #43 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > stress D c04b41e8 0 2116 2115 0x00000000 > [<c04b41e8>] (__schedule) from [<c04b46dc>] (schedule+0x40/0x90) > [<c04b46dc>] (schedule) from [<c04b6ec8>] (__down_read+0xc4/0xfc) > [<c04b6ec8>] (__down_read) from [<c04b69c0>] (down_read+0x18/0x1c) > [<c04b69c0>] (down_read) from [<c001d41c>] (do_page_fault+0xac/0x420) > [<c001d41c>] (do_page_fault) from [<c0008444>] (do_DataAbort+0x44/0xa8) > [<c0008444>] (do_DataAbort) from [<c00136b8>] (__dabt_svc+0x38/0x60) > Exception stack(0xecbc3af8 to 0xecbc3b40) > 3ae0: ecbc3b74 b6d72ff4 > 3b00: ffffffec 00000000 b6d72ff4 ec0fc000 00000000 ec0fc000 0000007e 00000000 > 3b20: ecbc2000 ecbc3bac 00000014 ecbc3b44 c0019e78 c021ef44 00000013 ffffffff > [<c00136b8>] (__dabt_svc) from [<c021ef44>] (__copy_from_user+0xa4/0x3a0) > > Signed-off-by: Jean Pihet <jean.pihet@linaro.org> > Cc: Will Deacon <will.deacon@arm.com> > --- > arch/arm/kernel/perf_event.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c > index 6493c4c..f5aeca2 100644 > --- a/arch/arm/kernel/perf_event.c > +++ b/arch/arm/kernel/perf_event.c > @@ -560,11 +560,16 @@ user_backtrace(struct frame_tail __user *tail, > struct perf_callchain_entry *entry) > { > struct frame_tail buftail; > + unsigned long err; > > - /* Also check accessibility of one struct frame_tail beyond */ > if (!access_ok(VERIFY_READ, tail, sizeof(buftail))) > return NULL; > - if (__copy_from_user_inatomic(&buftail, tail, sizeof(buftail))) > + > + pagefault_disable(); > + err = __copy_from_user_inatomic(&buftail, tail, sizeof(buftail)); > + pagefault_enable(); > + > + if (err) > return NULL; > > perf_callchain_store(entry, buftail.lr); > -- > 1.8.1.2 > >
Hi Will, On 3 July 2014 19:52, Will Deacon <will.deacon@arm.com> wrote: > Hi Jean, > > On Fri, Jun 27, 2014 at 03:57:46PM +0100, Jean Pihet wrote: >> As done on other architectures (ARM64, x86, Sparc etc.). >> >> This prevents a deadlock on down_read in do_page_fault when unwinding >> using fp and triggering on kernel tracepoints: > > So is this an issue because you could try setting tracepoints on the > pagefault path? If so, the patch is a little brutal as it would break user > backtracing as soon as we take any old page fault, no? > > Or am I missing something obvious? The problem is a deadlock between the perf events interrupt and copy_from_user, which take the same lock. The commit description has been updated to give all the details about it. Big thanks to Steve on the debugging! A new patch set is on its way. Jean > > Will > >> INFO: task stress:2116 blocked for more than 120 seconds. >> Not tainted 3.15.0-rc4-00364-g3401dfb-dirty #43 >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> stress D c04b41e8 0 2116 2115 0x00000000 >> [<c04b41e8>] (__schedule) from [<c04b46dc>] (schedule+0x40/0x90) >> [<c04b46dc>] (schedule) from [<c04b6ec8>] (__down_read+0xc4/0xfc) >> [<c04b6ec8>] (__down_read) from [<c04b69c0>] (down_read+0x18/0x1c) >> [<c04b69c0>] (down_read) from [<c001d41c>] (do_page_fault+0xac/0x420) >> [<c001d41c>] (do_page_fault) from [<c0008444>] (do_DataAbort+0x44/0xa8) >> [<c0008444>] (do_DataAbort) from [<c00136b8>] (__dabt_svc+0x38/0x60) >> Exception stack(0xecbc3af8 to 0xecbc3b40) >> 3ae0: ecbc3b74 b6d72ff4 >> 3b00: ffffffec 00000000 b6d72ff4 ec0fc000 00000000 ec0fc000 0000007e 00000000 >> 3b20: ecbc2000 ecbc3bac 00000014 ecbc3b44 c0019e78 c021ef44 00000013 ffffffff >> [<c00136b8>] (__dabt_svc) from [<c021ef44>] (__copy_from_user+0xa4/0x3a0) >> >> Signed-off-by: Jean Pihet <jean.pihet@linaro.org> >> Cc: Will Deacon <will.deacon@arm.com> >> --- >> arch/arm/kernel/perf_event.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c >> index 6493c4c..f5aeca2 100644 >> --- a/arch/arm/kernel/perf_event.c >> +++ b/arch/arm/kernel/perf_event.c >> @@ -560,11 +560,16 @@ user_backtrace(struct frame_tail __user *tail, >> struct perf_callchain_entry *entry) >> { >> struct frame_tail buftail; >> + unsigned long err; >> >> - /* Also check accessibility of one struct frame_tail beyond */ >> if (!access_ok(VERIFY_READ, tail, sizeof(buftail))) >> return NULL; >> - if (__copy_from_user_inatomic(&buftail, tail, sizeof(buftail))) >> + >> + pagefault_disable(); >> + err = __copy_from_user_inatomic(&buftail, tail, sizeof(buftail)); >> + pagefault_enable(); >> + >> + if (err) >> return NULL; >> >> perf_callchain_store(entry, buftail.lr); >> -- >> 1.8.1.2 >> >>
diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c index 6493c4c..f5aeca2 100644 --- a/arch/arm/kernel/perf_event.c +++ b/arch/arm/kernel/perf_event.c @@ -560,11 +560,16 @@ user_backtrace(struct frame_tail __user *tail, struct perf_callchain_entry *entry) { struct frame_tail buftail; + unsigned long err; - /* Also check accessibility of one struct frame_tail beyond */ if (!access_ok(VERIFY_READ, tail, sizeof(buftail))) return NULL; - if (__copy_from_user_inatomic(&buftail, tail, sizeof(buftail))) + + pagefault_disable(); + err = __copy_from_user_inatomic(&buftail, tail, sizeof(buftail)); + pagefault_enable(); + + if (err) return NULL; perf_callchain_store(entry, buftail.lr);
As done on other architectures (ARM64, x86, Sparc etc.). This prevents a deadlock on down_read in do_page_fault when unwinding using fp and triggering on kernel tracepoints: INFO: task stress:2116 blocked for more than 120 seconds. Not tainted 3.15.0-rc4-00364-g3401dfb-dirty #43 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. stress D c04b41e8 0 2116 2115 0x00000000 [<c04b41e8>] (__schedule) from [<c04b46dc>] (schedule+0x40/0x90) [<c04b46dc>] (schedule) from [<c04b6ec8>] (__down_read+0xc4/0xfc) [<c04b6ec8>] (__down_read) from [<c04b69c0>] (down_read+0x18/0x1c) [<c04b69c0>] (down_read) from [<c001d41c>] (do_page_fault+0xac/0x420) [<c001d41c>] (do_page_fault) from [<c0008444>] (do_DataAbort+0x44/0xa8) [<c0008444>] (do_DataAbort) from [<c00136b8>] (__dabt_svc+0x38/0x60) Exception stack(0xecbc3af8 to 0xecbc3b40) 3ae0: ecbc3b74 b6d72ff4 3b00: ffffffec 00000000 b6d72ff4 ec0fc000 00000000 ec0fc000 0000007e 00000000 3b20: ecbc2000 ecbc3bac 00000014 ecbc3b44 c0019e78 c021ef44 00000013 ffffffff [<c00136b8>] (__dabt_svc) from [<c021ef44>] (__copy_from_user+0xa4/0x3a0) Signed-off-by: Jean Pihet <jean.pihet@linaro.org> Cc: Will Deacon <will.deacon@arm.com> --- arch/arm/kernel/perf_event.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)