| Message ID | 20120209185043.GA12089@joshcartwright.net |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Feb 9, 2012 at 10:50 AM, Josh Cartwright <joshc@linux.com> wrote: > The locking policy is such that the erase_complete_block spinlock is > nested within the alloc_sem mutex. This fixes a case in which the > acquisition order was erroneously reversed. This issue was caught by > the following lockdep splat: (Bump.) Anybody interested in this patch? It seemed sane to me, and I had it sitting in my inbox. It does need a trivial rebase, BTW. Brian
On Thu, Mar 29, 2012 at 08:38:41AM -0700, Brian Norris wrote: > On Thu, Feb 9, 2012 at 10:50 AM, Josh Cartwright <joshc@linux.com> wrote: > > The locking policy is such that the erase_complete_block spinlock is > > nested within the alloc_sem mutex. This fixes a case in which the > > acquisition order was erroneously reversed. This issue was caught by > > the following lockdep splat: > > (Bump.) Anybody interested in this patch? It seemed sane to me, and I > had it sitting in my inbox. It does need a trivial rebase, BTW. I'm certainly still interested in it, for what its worth :). We've had no problems here for the month and a half its been in our tree. I'll send out a rebased V2. Thanks!
diff --git a/fs/jffs2/gc.c b/fs/jffs2/gc.c index 31dce61..4bbd521 100644 --- a/fs/jffs2/gc.c +++ b/fs/jffs2/gc.c @@ -225,8 +225,8 @@ int jffs2_garbage_collect_pass(struct jffs2_sb_info *c) return 0; D1(printk(KERN_DEBUG "No progress from erasing blocks; doing GC anyway\n")); - spin_lock(&c->erase_completion_lock); mutex_lock(&c->alloc_sem); + spin_lock(&c->erase_completion_lock); } /* First, work out which block we're garbage-collecting */
The locking policy is such that the erase_complete_block spinlock is nested within the alloc_sem mutex. This fixes a case in which the acquisition order was erroneously reversed. This issue was caught by the following lockdep splat: ======================================================= [ INFO: possible circular locking dependency detected ] 3.0.5 #1 ------------------------------------------------------- jffs2_gcd_mtd6/299 is trying to acquire lock: (&c->alloc_sem){+.+.+.}, at: [<c01f7714>] jffs2_garbage_collect_pass+0x314/0x890 but task is already holding lock: (&(&c->erase_completion_lock)->rlock){+.+...}, at: [<c01f7708>] jffs2_garbage_collect_pass+0x308/0x890 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&(&c->erase_completion_lock)->rlock){+.+...}: [<c008bec4>] validate_chain+0xe6c/0x10bc [<c008c660>] __lock_acquire+0x54c/0xba4 [<c008d240>] lock_acquire+0xa4/0x114 [<c046780c>] _raw_spin_lock+0x3c/0x4c [<c01f744c>] jffs2_garbage_collect_pass+0x4c/0x890 [<c01f937c>] jffs2_garbage_collect_thread+0x1b4/0x1cc [<c0071a68>] kthread+0x98/0xa0 [<c000f264>] kernel_thread_exit+0x0/0x8 -> #0 (&c->alloc_sem){+.+.+.}: [<c008ad2c>] print_circular_bug+0x70/0x2c4 [<c008c08c>] validate_chain+0x1034/0x10bc [<c008c660>] __lock_acquire+0x54c/0xba4 [<c008d240>] lock_acquire+0xa4/0x114 [<c0466628>] mutex_lock_nested+0x74/0x33c [<c01f7714>] jffs2_garbage_collect_pass+0x314/0x890 [<c01f937c>] jffs2_garbage_collect_thread+0x1b4/0x1cc [<c0071a68>] kthread+0x98/0xa0 [<c000f264>] kernel_thread_exit+0x0/0x8 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&(&c->erase_completion_lock)->rlock); lock(&c->alloc_sem); lock(&(&c->erase_completion_lock)->rlock); lock(&c->alloc_sem); *** DEADLOCK *** 1 lock held by jffs2_gcd_mtd6/299: #0: (&(&c->erase_completion_lock)->rlock){+.+...}, at: [<c01f7708>] jffs2_garbage_collect_pass+0x308/0x890 stack backtrace: [<c00155dc>] (unwind_backtrace+0x0/0x100) from [<c0463dc0>] (dump_stack+0x20/0x24) [<c0463dc0>] (dump_stack+0x20/0x24) from [<c008ae84>] (print_circular_bug+0x1c8/0x2c4) [<c008ae84>] (print_circular_bug+0x1c8/0x2c4) from [<c008c08c>] (validate_chain+0x1034/0x10bc) [<c008c08c>] (validate_chain+0x1034/0x10bc) from [<c008c660>] (__lock_acquire+0x54c/0xba4) [<c008c660>] (__lock_acquire+0x54c/0xba4) from [<c008d240>] (lock_acquire+0xa4/0x114) [<c008d240>] (lock_acquire+0xa4/0x114) from [<c0466628>] (mutex_lock_nested+0x74/0x33c) [<c0466628>] (mutex_lock_nested+0x74/0x33c) from [<c01f7714>] (jffs2_garbage_collect_pass+0x314/0x890) [<c01f7714>] (jffs2_garbage_collect_pass+0x314/0x890) from [<c01f937c>] (jffs2_garbage_collect_thread+0x1b4/0x1cc) [<c01f937c>] (jffs2_garbage_collect_thread+0x1b4/0x1cc) from [<c0071a68>] (kthread+0x98/0xa0) [<c0071a68>] (kthread+0x98/0xa0) from [<c000f264>] (kernel_thread_exit+0x0/0x8) Signed-off-by: Josh Cartwright <joshc@linux.com> --- fs/jffs2/gc.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)