Re: VFS deadlock ?

[Dave Jones]

On Thu, Mar 21, 2013 at 07:21:46PM +0000, Al Viro wrote:
 > On Thu, Mar 21, 2013 at 03:06:53PM -0400, Dave Jones wrote:
 > > Al, Linus,
 > 
 > > trinity-child2  D ffff880110b3a7e0  5448  7669      1 0x00000004
 > [sits in rename(), trying to grab ->i_mutex on a parent]
 > 
 > > Showing all locks held in the system:
 > > 4 locks on stack by trinity-child2/7669:
 > >  #0: blocked:  (sb_writers#4){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
 > >  #1: held:     (&type->s_vfs_rename_key){+.+.+.}, instance: ffff8801292d1928, at: [<ffffffff811c6f5e>] lock_rename+0x3e/0x120
 > >  #2: held:     (&type->i_mutex_dir_key#2/1){+.+.+.}, instance: ffff880110b3a858, at: [<ffffffff811c701e>] lock_rename+0xfe/0x120
 > >  #3: blocked:  (&type->i_mutex_dir_key#2/2){+.+.+.}, instance: ffff880110b3a858, at: [<ffffffff811c7034>] lock_rename+0x114/0x120
 > 
 > Wait a minute...  How the hell does it manage to sit with *two* blocked locks?
 > Confused...

Same thing happened when I ran into this yesterday..
(bit more confusing, as there were more parallel runs going on, but similar patterns..)


Showing all locks held in the system:
1 lock on stack by trinity-main/784:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
2 locks on stack by trinity-child3/6674:
 #0: blocked:  (sb_writers#5){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
 #1: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811ba1d9>] chmod_common+0x49/0xa0
1 lock on stack by trinity-child3/9678:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
1 lock on stack by trinity-child0/9845:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
2 locks on stack by trinity-child1/10147:
 #0: blocked:  (sb_writers#5){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
 #1: blocked:  (&type->i_mutex_dir_key#2/1){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811c9ffd>] kern_path_create+0xad/0x190
1 lock on stack by trinity-child2/10793:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811cb5da>] do_last+0x33a/0xf20
1 lock on stack by trinity-child1/11549:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
4 locks on stack by trinity-child0/11592:
 #0: blocked:  (sb_writers#5){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
 #1: held:     (&type->s_vfs_rename_key){+.+.+.}, instance: ffff8801292d1928, at: [<ffffffff811c6f5e>] lock_rename+0x3e/0x120
 #2: held:     (&type->i_mutex_dir_key#2/1){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811c701e>] lock_rename+0xfe/0x120
 #3: blocked:  (&type->i_mutex_dir_key#2/2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811c7034>] lock_rename+0x114/0x120
1 lock on stack by trinity-child0/11645:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
2 locks on stack by trinity-child3/11740:
 #0: blocked:  (sb_writers#5){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
 #1: blocked:  (&type->i_mutex_dir_key#2/1){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811c9ffd>] kern_path_create+0xad/0x190
1 lock on stack by trinity-child2/11953:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
1 lock on stack by trinity-child2/12018:
 #0: blocked:  (&type->i_mutex_dir_key#2){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff816bb512>] lookup_slow+0x13f/0x1b8
2 locks on stack by trinity-child1/12312:
 #0: blocked:  (sb_writers#5){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
 #1: blocked:  (&type->i_mutex_dir_key#2/1){+.+.+.}, instance: ffff88010c1717c0, at: [<ffffffff811caaa2>] do_unlinkat+0x112/0x230


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