Messages in this thread | | | Date | Thu, 27 Nov 2008 08:27:51 +0200 | From | Benny Halevy <> | Subject | Re: WARN_ON out of range error in ERR_PTR? |
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On Nov. 27, 2008, 2:15 +0200, Andrew Morton <akpm@linux-foundation.org> wrote: > On Wed, 26 Nov 2008 17:48:08 +0200 > Benny Halevy <bhalevy@panasas.com> wrote: > >> Andrew, >> >> After hitting a bug where an nfs error -10021 wasn't handled >> correctly since IS_ERR returned false on its ERR_PTR value > > That sounds like an error in NFS. Did it get fixed?
Right, it is an error I made when developing new code for nfs41 and I caught and fixed it in my branch before releasing the code. I just thought that this WARN_ON could be beneficial for everybody...
Benny
> >> I realized that adding a BUG_ON to make sure the mapped error >> is in the valid range would have caught this. >> >> Since ERR_PTR is not called on the critical path >> (unlike IS_ERR) but rather on the error handling path I believe >> we can tolerate the extra cost. >> >> The reason this is just a WARN_ON and not BUG_ON is to make >> fixing it easier, although I do consider calling ERR_PTR on an >> out of range error a pretty dangerous bug as the error might go >> unnoticed. >> >> How about committing the following patch to -mm? >> >> Signed-off-by: Benny Halevy <bhalevy@panasas.com> >> --- >> include/linux/err.h | 3 ++- >> 1 files changed, 2 insertions(+), 1 deletions(-) >> >> diff --git a/include/linux/err.h b/include/linux/err.h >> index ec87f31..81df84f 100644 >> --- a/include/linux/err.h >> +++ b/include/linux/err.h >> @@ -2,7 +2,7 @@ >> #define _LINUX_ERR_H >> >> #include <linux/compiler.h> >> - >> +#include <asm/bug.h> >> #include <asm/errno.h> >> >> /* >> @@ -21,6 +21,7 @@ >> >> static inline void *ERR_PTR(long error) >> { >> + WARN_ON(error && !IS_ERR_VALUE(error)); >> return (void *) error; >> } > > We have over 2000 ERR_PTR callsites, and WARN_ON() is a big fat porky > thing, so this change would add quite a lot of kernel text&data. > > If this problem does occur again, I expect that the kernel will > reliably dereference a small negative address and we'll get an oops, > which will give us the same information as that WARN_ON would have > done, no? > > >
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