Linus Torvalds 5f22ca9b13 vfat: fix 'sync' mount deadlock due to BKL->lock_super conversion ... There was another FAT BKL conversion deadlock reported by Bart Trojanowski due to the BKL being used as a recursive lock by FAT, which was missed because it only triggers with 'sync' (or 'dirsync') mounts. The recursion worked for the BKL, but after the conversion to lock_super (which uses a mutex), it just deadlocks. Thanks to Bart for debugging this and testing the fix. The lock debugging information from the original report: ============================================= [ INFO: possible recursive locking detected ] 2.6.27-rc3-bisect-00448-ga7f5aaf #16 --------------------------------------------- mv/4020 is trying to acquire lock: (&type->s_lock_key#9){--..}, at: [<c01a90fe>] lock_super+0x1e/0x20 but task is already holding lock: (&type->s_lock_key#9){--..}, at: [<c01a90fe>] lock_super+0x1e/0x20 other info that might help us debug this: 3 locks held by mv/4020: #0: (&sb->s_type->i_mutex_key#9/1){--..}, at: [<c01b2336>] do_unlinkat+0x66/0x140 #1: (&sb->s_type->i_mutex_key#9){--..}, at: [<c01b0954>] vfs_unlink+0x84/0x110 #2: (&type->s_lock_key#9){--..}, at: [<c01a90fe>] lock_super+0x1e/0x20 stack backtrace: Pid: 4020, comm: mv Not tainted 2.6.27-rc3-bisect-00448-ga7f5aaf #16 [<c014e694>] validate_chain+0x984/0xea0 [<c0108d70>] ? native_sched_clock+0x0/0xf0 [<c014ee9c>] __lock_acquire+0x2ec/0x9b0 [<c014f5cf>] lock_acquire+0x6f/0x90 [<c01a90fe>] ? lock_super+0x1e/0x20 [<c044e5fd>] mutex_lock_nested+0xad/0x300 [<c01a90fe>] ? lock_super+0x1e/0x20 [<c01a90fe>] ? lock_super+0x1e/0x20 [<c01a90fe>] lock_super+0x1e/0x20 [<f8b3a700>] fat_write_inode+0x60/0x2b0 [fat] [<c0450878>] ? _spin_unlock_irqrestore+0x48/0x80 [<f8b3a953>] ? fat_sync_inode+0x3/0x20 [fat] [<f8b3a962>] fat_sync_inode+0x12/0x20 [fat] [<f8b37c7e>] fat_remove_entries+0xbe/0x120 [fat] [<f8b422ef>] vfat_unlink+0x5f/0x90 [vfat] [<f8b42290>] ? vfat_unlink+0x0/0x90 [vfat] [<c01b0968>] vfs_unlink+0x98/0x110 [<c01b2400>] do_unlinkat+0x130/0x140 [<c016a8f5>] ? audit_syscall_entry+0x105/0x150 [<c01b253b>] sys_unlinkat+0x3b/0x40 [<c01040d3>] sysenter_do_call+0x12/0x3f ======================= where the deadlock is due to the nesting of lock_super from vfat_unlink to fat_write_inode: - do_unlinkat - vfs_unlink - vfat_unlink * lock_super - fat_remove_entries - fat_sync_inode - fat_write_inode * lock_super and the fix is to simply remove the use of lock_super() in fat_write_inode. The lock_super() there had been just an automatic conversion of the kernel lock to the superblock lock, but no locking was actually needed there, since the code in fat_write_inode already protected all relevant accesses with a spinlock (sbi->inode_hash_lock to be exact). The only code inside the BKL (and thus the superblock lock) was accesses tp local variables or calls to functions that have long been SMP-safe (i.e. sb_bread, mark_buffe_dirty and brlese). Bart reports: "Looks good. I ran 10 parallel processes creating 1M files truncating them, writing to them again and then deleting them. This patch fixes the issue I ran into. Signed-off-by: Bart Trojanowski <bart@jukie.net>" Reported-and-tested-by: Bart Trojanowski <bart@jukie.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2008-08-20 08:31:19 -07:00
..
cache.c
dir.c
fatent.c
file.c
inode.c
Makefile
misc.c