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Gmane
From: Jason Lunz <lunz <at> falooley.org>
Subject: jffs2 deadlock introduced in linux 2.6.22.5
Newsgroups: gmane.linux.file-systems.jffs
Date: Thursday 30th August 2007 18:23:55 UTC (over 10 years ago)
commit 1d8715b388c978b0f1b1bf4812fcee0e73b023d7 was added between
2.6.22.4 and 2.6.22.5 to cure a locking problem, but it seems to have
introduced another (worse?) one.

With a jffs2 filesystem (on block2mtd) on a 2.6.22.5 kernel, if I do
anything that appends to a file with many small writes, I get what looks
like a deadlock between the writer and the jffs2 gc thread. For example:

	# while true; do echo >> /some/file/on/jffs2; done

will result in the bash hanging in D state, with these kernel stacks in
dmesg after "echo t > /proc/sysrq-trigger":

jffs2_gcd_mtd S DFD1EEA8     0  1086      2 (L-TLB)
       dfd1eebc 00000046 00000002 dfd1eea8 dfd1eea4 00000000 00000000
c0334a00 
       c0334a00 00000000 0000000a dfcb8550 2ee3df10 0000001a 00002280
dfcb8670 
       c1407a00 00000000 00000286 df9fa600 dfe20900 ffff414a c1407ec4
0000ffff 
Call Trace:
 [] __down_interruptible+0xb2/0x10b
 [] __sched_text_start+0x14b/0x8a4
 [] default_wake_function+0x0/0xc
 [] __down_failed_interruptible+0x7/0xc
 [] jffs2_garbage_collect_pass+0x20/0x597 [jffs2]
 [] __dequeue_signal+0xd7/0x11c
 [] recalc_sigpending+0xb/0x1d
 [] dequeue_signal+0x9d/0x117
 [] jffs2_garbage_collect_thread+0x11b/0x15a [jffs2]
 [] ret_from_fork+0x6/0x1c
 [] jffs2_garbage_collect_thread+0x0/0x15a [jffs2]
 [] jffs2_garbage_collect_thread+0x0/0x15a [jffs2]
 [] kernel_thread_helper+0x7/0x10

bash          D CE2C85E0     0  2223   2219 (NOTLB)
       d834bb2c 00000086 00000000 ce2c85e0 ce2c85e0 ce8004c0 00000003
c0334a00 
       c0334a00 00000000 00000009 df93ca70 2ee3bc90 0000001a 0002ff74
df93cb90 
       c1407a00 00000000 00000000 00000000 dfe20900 00000000 c1407ec4
00000000 
Call Trace:
 [] io_schedule+0x1e/0x28
 [] sync_page+0x38/0x3b
 [] __wait_on_bit+0x33/0x58
 [] sync_page+0x0/0x3b
 [] wait_on_page_bit+0x63/0x69
 [] wake_bit_function+0x0/0x3c
 [] read_cache_page+0x28/0x3f
 [] jffs2_gc_fetch_page+0x26/0x3b [jffs2]
 [] jffs2_garbage_collect_live+0x992/0xf87 [jffs2]
 [] block2mtd_write+0x18f/0x1a6 [block2mtd]
 [] default_mtd_writev+0x0/0x9e [mtdcore]
 [] jffs2_flash_direct_writev+0x62/0xd0 [jffs2]
 [] jffs2_garbage_collect_pass+0x4ff/0x597 [jffs2]
 [] aufs_read_unlock+0x17/0x5f [aufs]
 [] ibend+0x39/0x3f [aufs]
 [] jffs2_reserve_space+0xb5/0x15b [jffs2]
 [] send_sig_info+0x55/0x65
 [] jffs2_write_inode_range+0x5a/0x278 [jffs2]
 [] jffs2_commit_write+0xec/0x1be [jffs2]
 [] generic_file_buffered_write+0x3f1/0x5af
 [] dput+0x15/0xda
 [] __link_path_walk+0xb2d/0xc0e
 [] current_fs_time+0x41/0x46
 [] __generic_file_aio_write_nolock+0x479/0x4c8
 [] link_path_walk+0xa9/0xb3
 [] generic_file_aio_write+0x61/0xc2
 [] permission+0xc8/0xdb
 [] do_sync_write+0x0/0x10a
 [] do_sync_write+0xc7/0x10a
 [] open_namei+0x254/0x571
 [] autoremove_wake_function+0x0/0x33
 [] do_sync_write+0x0/0x10a
 [] vfs_write+0xa8/0x130
 [] sys_write+0x41/0x67
 [] syscall_call+0x7/0xb

Given that I never saw any jffs2 deadlocks in other 2.6.22 kernels,
maybe that commit should be reverted until a better solution is found?

Jason
 
CD: 17ms