Hello, We saw a crash at the following line in mdcache_get_chunk() as prev_chunk's dirent list is empty. chunk->reload_ck = glist_last_entry(&prev_chunk->dirents, mdcache_dir_entry_t, chunk_list)->ck; The backtrace of the coredump is at the end of the mail. I could reproduce similar crash by doing the following: 1. In mdcache_readdir_chunked inserted a sleep(30) after the content_lock is released and before the content_lock is acquired for writing as follows: 2805 again: 2806 /* Get here on first pass, retry if we don't hold the write lock, 2807 * and repeated passes if we need to fetch another chunk. 2808 */ 2809 2810 LogFullDebugAlt(COMPONENT_NFS_READDIR, COMPONENT_CACHE_INODE, 2811 "Readdir chunked next_ck=0x%"PRIx64" look_ck=%"PRIx64, 2812 next_ck, look_ck); 2813 2814 if (look_ck == 0 || 2815 !mdcache_avl_lookup_ck(directory, look_ck, &dirent)) { 2816 fsal_status_t status; 2817 /* This starting position isn't in our cache... 2818 * Go populate the cache and process from there. 2819 */ 2820 if (!has_write) { 2821 /* Upgrade to write lock and retry just in case 2822 * another thread managed to populate this cookie 2823 * in the meantime. 2824 */ 2825 PTHREAD_RWLOCK_unlock(&directory-> content_lock); 2826 sleep (30); // Sleep here 2827 PTHREAD_RWLOCK_wrlock(&directory-> content_lock); 2828 has_write = true; 2829 goto again; 2830 } 2. From 1st client run 'ls' inside a mounted directory for an export. 'ls' is made to wait as there is sleep() in mdcache_readdir_chunked() 3. Immediately from 2nd client remove all the entries inside the mounted directory for the same export. 4. After sleep() time is over, ganesha crashes as the 'prev_chunk' is not valid in mdcache_readdir_chunked() Following is the coredump for reference. The code used was ganesha 2.5 and it has patches for 'readdir' taken from https://github.com/dang/nfs-ganesha/tree/v2.5-readdir, the code for mdcache_readdir_chunked() looks similar to mdcache_readdir_chunked() in 2.8 #0 0x00007fae938dc4ab in raise () from /lib64/libpthread.so.0 #1 0x000000000045549e in crash_handler (signo=11, info=0x7fae25f48eb0, ctx=0x7fae25f48d80) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/MainNFSD/nfs_init.c:225 #2 <signal handler called> #3 mdcache_get_chunk (parent=0x7faa1001a290, prev_chunk=0x7fade0206350, whence=2147483647) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/FSAL/Stackable_FSALs/FSAL_MDCACHE/mdcache_lru.c:909 #4 0x000000000054fbe9 in mdcache_populate_dir_chunk (directory=0x7faa1001a290, whence=2147483647, dirent=0x7fae25f49680, prev_chunk=0x7fade0206350, eod_met=0x7fae25f4967f) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/FSAL/Stackable_FSALs/FSAL_MDCACHE/mdcache_helpers.c:2659 #5 0x0000000000551767 in mdcache_readdir_chunked (directory=0x7faa1001a290, whence=2147483647, dir_state=0x7fae25f49990, cb=0x43310f <populate_dirent>, attrmask=0, eod_met=0x7fae25f49e8b) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/FSAL/Stackable_FSALs/FSAL_MDCACHE/mdcache_helpers.c:3053 #6 0x000000000053f39f in mdcache_readdir (dir_hdl=0x7faa1001a2c8, whence=0x7fae25f49970, dir_state=0x7fae25f49990, cb=0x43310f <populate_dirent>, attrmask=0, eod_met=0x7fae25f49e8b) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/FSAL/Stackable_FSALs/FSAL_MDCACHE/mdcache_handle.c:639 #7 0x00000000004339f3 in fsal_readdir (directory=0x7faa1001a2c8, cookie=2147483647, nbfound=0x7fae25f49e8c, eod_met=0x7fae25f49e8b, attrmask=0, cb=0x495d70 <nfs3_readdir_callback>, opaque=0x7fae25f49e40) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/FSAL/fsal_helper.c:1502 #8 0x0000000000495b57 in nfs3_readdir (arg=0x7fa8b4f75e80, req=0x7fa8b4f75678, res=0x7faad82c8c70) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/Protocols/NFS/nfs3_readdir.c:289 #9 0x000000000044ccde in nfs_rpc_execute (reqdata=0x7fa8b4f75650) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/MainNFSD/nfs_worker_thread.c:1290 #10 0x000000000044d4e8 in worker_run (ctx=0x4926600) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/MainNFSD/nfs_worker_thread.c:1562 #11 0x000000000050c57f in fridgethr_start_routine (arg=0x4926600) at /usr/src/debug/nfs-ganesha-2.5.3-ibm031.00-0.1.1-Source/support/fridgethr.c:550 (gdb) frame 3 (gdb) p *prev_chunk $9 = {chunks = {next = 0x7faad808a570, prev = 0x7fade00000d8}, dirents = {next = 0x7fade0206360, prev = 0x7fade0206360}, parent = 0x0, chunk_lru = {q = {next = 0x0, prev = 0x0}, qid = LRU_ENTRY_L1, refcnt = 0, flags = 0, lane = 534, cf = 0}, reload_ck = 1453366958, next_ck = 0, num_entries = 112} To fix this I have posted a patch: https://review.gerrithub.io/c/ffilz/nfs-ganesha/+/440079 Thanks, Madhu Thorat.