[Gluster-devel] Segfault at cache read_dir

Shehjar Tikoo shehjart at gluster.com
Wed Nov 25 06:20:06 UTC 2009


Dongmin Yu wrote:
> Hello
> 
>  
> 
> I’m using GlusterFS-2.0.8 and I turn on readahead. I got a Segfault when 
> I try to read a directory.
> 
> At the following trace, fd_ctx->dcache seems to be NULL
> 
>  
> 
>  
> 
> volume readahead
> 
>   type performance/read-ahead
> 
>   option page-count 4           # 2 is default option
> 
>   option force-atime-update off # default is off
> 
>   subvolumes distribute
> 
> end-volume
> 
>  
> 
>  
> 
>  
> 
> Program received signal SIGSEGV, Segmentation fault.
> 
> 0x00002aaab4b03606 in libgf_dcache_readdir (ctx=<value optimized out>,
> 
>     fd=<value optimized out>, dirp=0x2aaab31cd7f8, offset=0x4f9d2248)
> 
>     at libglusterfsclient.c:398
> 
> 398             *offset = fd_ctx->dcache->next->d_off;
> 
> (gdb) bt
> 
> #0  0x00002aaab4b03606 in libgf_dcache_readdir (ctx=<value optimized out>,
> 
>     fd=<value optimized out>, dirp=0x2aaab31cd7f8, offset=0x4f9d2248)
> 
>     at libglusterfsclient.c:398
> 
> #1  0x00002aaab4b100d9 in libgf_client_readdir (ctx=0x2aaab31cd80b,
> 
>     fd=0x2aaab48e0928, dirp=0x0, offset=0x0) at libglusterfsclient.c:4151
> 
> #2  0x00002aaab4b1047f in glusterfs_readdir (dirfd=0x2aaab319b310)
> 
>     at libglusterfsclient.c:4253
> 
> #3  0x00002aaab48e7e38 in gluster_readdir (self=<value optimized out>,
> 
>     args=0x2aaab4824840) at glusterfs.c:1035
> 
>  
> 
> (gdb) p  fd_ctx->dcache->next->d_off
> 
> Cannot access memory at address 0xb8
> 
> (gdb) p  fd_ctx
> 
> $1 = (libglusterfs_client_fd_ctx_t *) 0x2aaab31cd7c0
> 
> (gdb) p  fd_ctx->dcache
> 
> $2 = (struct direntcache *) 0x0


This should not be happening at this point. There are enough checks
for NULL before we reach this line. Is the application you are using
doing directory reading through multiple threads?



-Shehjar

> 
>  
> 
>  
> 
> *DongMin Yu*
> 
>  
> 
> HOSTWAY IDC Corp. / R&D Principal Researcher
> 
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> 
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