(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface). On Wed, 1 Apr 2009 12:31:51 GMT bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > http://bugzilla.kernel.org/show_bug.cgi?id=12995 > > Summary: NFS mount from avr32 platform crashes on 2.6.29 > Product: File System > Version: 2.5 > Platform: All > OS/Version: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: NFS > AssignedTo: trond.myklebust@xxxxxxxxxx > ReportedBy: brm@xxxxxxxxxx > Regression: No > > > The problem turns out to be in the recent(ish) changes in lockd. > > Specifically this struct definition > > struct nsm_handle { > struct list_head sm_link; > atomic_t sm_count; > char *sm_mon_name; > char *sm_name; > struct sockaddr_storage sm_addr; > size_t sm_addrlen; > unsigned int sm_monitored : 1, > sm_sticky : 1; /* don't unmonitor */ > struct nsm_private sm_priv; > char sm_addrbuf[NSM_ADDRBUF]; > }; > > results in my avr32 compiler (and my ia64 compiler) in aligning the sm_priv > structure (which is a char array) on an odd boundary. The subsequent use > of this field typecast to a u64 (nsm_init_private) as part of an nfs mount > causes a crash with unaligned access. > > The compiler only allocates *one byte* to the two bit bitfield. > Moving the bitfield to the end of the structure fixes the problem in my case. > It seems to me that one should be very careful with typecasting this sm_priv > data to anything with larger alignment but especially to a 64 bit type since > (at least on a 64 bit system) this may demand 64 bit alignment. > > In any case it looks like (with newer gcc at least) that bitfields are > extremely dangerous. > > Perhaps the solution is to malloc the nsm_private data and sm_priv is then a > pointer to this data. This would guarantee the correct alignment. > nsm_private is: struct nsm_private { unsigned char data[SM_PRIV_SIZE]; }; so the compiler is permitted to byte-align this. I assume that some code somewhere is accessing this with a larger-than-one-byte typecast? (Your bug report isn't complete - if it had included the trace then I'd know where the crash is occurring!) If so then something like this: --- a/include/linux/lockd/xdr.h~a +++ a/include/linux/lockd/xdr.h @@ -9,6 +9,7 @@ #ifndef LOCKD_XDR_H #define LOCKD_XDR_H +#include <linux/compiler.h> #include <linux/fs.h> #include <linux/nfs.h> #include <linux/sunrpc/xdr.h> @@ -16,9 +17,10 @@ #define SM_MAXSTRLEN 1024 #define SM_PRIV_SIZE 16 +/* suitable comment about the __aligned goes here */ struct nsm_private { unsigned char data[SM_PRIV_SIZE]; -}; +} __aligned(sizeof(unsigned long)); struct svc_rqst; would be an appropriate fix, as it actually expresses what's going on. If you agree then please cook up and test a patch? Please send the patch via email - we very much try to avoid merging patches out of bugzilla. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
