Hi, Chris Mason > -----Original Message----- > From: Chris Mason [mailto:clm@xxxxxx] > Sent: Thursday, January 21, 2016 10:15 PM > To: Zhao Lei <zhaolei@xxxxxxxxxxxxxx> > Cc: linux-btrfs@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 1/2] btrfs: reada: limit max works count > > On Thu, Jan 21, 2016 at 06:06:21PM +0800, Zhao Lei wrote: > > Hi, Chris Mason > > > > > -----Original Message----- > > > From: Chris Mason [mailto:clm@xxxxxx] > > > Sent: Thursday, January 21, 2016 1:48 AM > > > To: Zhao Lei <zhaolei@xxxxxxxxxxxxxx>; linux-btrfs@xxxxxxxxxxxxxxx > > > Subject: Re: [PATCH 1/2] btrfs: reada: limit max works count > > > > > > On Wed, Jan 20, 2016 at 10:16:27AM -0500, Chris Mason wrote: > > > > On Tue, Jan 12, 2016 at 03:46:26PM +0800, Zhao Lei wrote: > > > > > reada create 2 works for each level of tree in recursion. > > > > > > > > > > In case of a tree having many levels, the number of created > > > > > works is 2^level_of_tree. > > > > > Actually we don't need so many works in parallel, this patch > > > > > limit max works to BTRFS_MAX_MIRRORS * 2. > > > > > > > > Hi, > > > > > > > > I don't think you end up calling atomic_dec() for every time that > > > > reada_start_machine() is called. Also, I'd rather not have a > > > > global static variable to limit the parallel workers, when we have > > > > more than one FS mounted it'll end up limiting things too much. > > > > > > > > With this patch applied, I'm seeing deadlocks during btrfs/066. You > > > > have to run the scrub tests as well, basically we're just getting > > > > fsstress run alongside scrub. > > > > > > > > I'll run a few more times with it reverted to make sure, but I > > > > think it's the root cause. > > > > > > I spoke too soon, it ended up deadlocking a few tests later. > > > > > In logic, even if the calculation of atomic_dec() in this patch having > > bug, in worst condition, reada will works in single-thread mode, and > > will not introduce deadlock. > > > > And by looking the backtrace in this mail, maybe it is caused by > > reada_control->elems in someplace of this patchset. > > > > I recheck xfstests/066 in both vm and physical machine, on top of my > > pull-request git today, with btrfs-progs 4.4 for many times, but had not > triggered the bug. > > Just running 066 alone doesn't trigger it for me. I have to run everything from > 00->066. > > My setup is 5 drives. I use a script to carve them up into logical volumes, 5 for > the test device and 5 for the scratch pool. I think it should reproduce with a > single drive, if you still can't trigger I'll confirm that. > > > > > Could you tell me your test environment(TEST_DEV size, mount option), > > and odds of fails in btrfs/066? > > 100% odds of failing, one time it made it up to btrfs/072. I think more > important than the drive setup is that I have all the debugging on. > CONFIG_DEBUG_PAGEALLOC, spinlock debugging, mutex debugging and lock > dep enabled. > Thanks for your answer. But unfortunately I hadn't reproduce the dead_lock in above way today... Now I queued loop of above reproduce script in more nodes, and hopes it can happen in this weekend. And by reviewing code, I found a problem which can introduce similar bad result in logic, and made a patch for it. [PATCH] [RFC] btrfs: reada: avoid undone reada extents in btrfs_reada_wait Because it is only a problem in logic, but rarely happened, I only confirmed no-problem after patch applied. Sorry for increased your works, could you apply this patch and test is it works? Thanks Zhaolei > -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
