* [uml-devel] "Sleeping in atomic section" with ubd aio patch @ 2005-09-13 18:01 Blaisorblade 2005-09-14 19:22 ` [uml-devel] " Jeff Dike 0 siblings, 1 reply; 5+ messages in thread From: Blaisorblade @ 2005-09-13 18:01 UTC (permalink / raw) To: Jeff Dike; +Cc: user-mode-linux-devel Today I was running latest 2.6 UML git snapshot I have (from 8 September), compiled with spinlock debugging, and got a big number of long series of traces like this one (they varied a bit, but the core is do_io->kmem_cache_alloc). It's just because things are called under spinlocks and GFP_KERNEL is used - but if possible, it'd be better to use something better than GFP_ATOMIC (since this is performance critical). Debug: sleeping function called from invalid context at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/mm/slab.c:2097 in_atomic():0, irqs_disabled():1 a05bb5f0: [<a0015c52>] dump_stack+0x22/0x30 a05bb610: [<a0048ddc>] __might_sleep+0xac/0xd0 a05bb630: [<a0094a38>] kmem_cache_alloc+0x98/0xb0 a05bb660: [<a003b266>] do_io+0x3b6/0x520 a05bb760: [<a003a6ba>] do_ubd_request+0x12a/0x180 a05bb7f0: [<a01d146d>] __generic_unplug_device+0x2d/0x40 a05bb800: [<a01d1500>] generic_unplug_device+0x80/0x180 a05bb830: [<a01d1621>] blk_backing_dev_unplug+0x21/0x30 a05bb840: [<a00bca6a>] block_sync_page+0x3a/0x50 a05bb850: [<a0087556>] sync_page+0x46/0x60 a05bb860: [<a02c79e9>] __wait_on_bit_lock+0x49/0x70 a05bb880: [<a0087e39>] __lock_page+0x89/0xa0 a05bb900: [<a008866a>] do_generic_mapping_read+0x3ca/0x770 a05bb9e0: [<a0088e5e>] __generic_file_aio_read+0x26e/0x2c0 a05bba60: [<a0088f03>] generic_file_aio_read+0x53/0x90 a05bba90: [<a00b53bc>] do_sync_read+0xdc/0x130 a05bbb60: [<a00b54f3>] vfs_read+0xe3/0x290 a05bbba0: [<a00b5a2b>] sys_read+0x4b/0x80 a05bbbd0: [<a001e687>] handle_syscall+0x117/0x140 a05bbc70: [<a001d5a6>] userspace+0x236/0x3c0 a05bbcf0: [<a001e1d8>] fork_handler+0xb8/0xd0 a05bbd20: [<ffffe420>] _etext+0x5fd3398a/0x0 -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it ------------------------------------------------------- SF.Net email is Sponsored by the Better Software Conference & EXPO September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel ^ permalink raw reply [flat|nested] 5+ messages in thread
* [uml-devel] Re: "Sleeping in atomic section" with ubd aio patch 2005-09-13 18:01 [uml-devel] "Sleeping in atomic section" with ubd aio patch Blaisorblade @ 2005-09-14 19:22 ` Jeff Dike 2005-09-14 20:00 ` Blaisorblade 0 siblings, 1 reply; 5+ messages in thread From: Jeff Dike @ 2005-09-14 19:22 UTC (permalink / raw) To: Blaisorblade; +Cc: user-mode-linux-devel On Tue, Sep 13, 2005 at 08:01:40PM +0200, Blaisorblade wrote: > It's just because things are called under spinlocks and GFP_KERNEL is used - > but if possible, it'd be better to use something better than GFP_ATOMIC > (since this is performance critical). This would be ubd_io_lock, which is taken for us by the block layer before entering do_ubd_request. We could make that a GFP_ATOMIC allocation, except that we have already dequeued the request, so would need to do something with it if the allocation failed. I'm wondering if we can drop the lock before do_io and pick it up afterwards. The bitmap argument is a global, which is a problem. Two racing requests could result in one writing out a bitmap which is either too old or too new. So, I'm not sure how to handle this. We could requeue what's left of the request if an allocation failure happens. We could drop the lock and pick it up later, but we have to be careful to write out the current bitmap, not one which we saved earlier or one which has been updated to reflect a racing request which is coming through later. Jeff ------------------------------------------------------- SF.Net email is sponsored by: Tame your development challenges with Apache's Geronimo App Server. Download it for free - -and be entered to win a 42" plasma tv or your very own Sony(tm)PSP. Click here to play: http://sourceforge.net/geronimo.php _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel ^ permalink raw reply [flat|nested] 5+ messages in thread
* [uml-devel] Re: "Sleeping in atomic section" with ubd aio patch 2005-09-14 19:22 ` [uml-devel] " Jeff Dike @ 2005-09-14 20:00 ` Blaisorblade 2005-09-14 21:18 ` Jeff Dike 0 siblings, 1 reply; 5+ messages in thread From: Blaisorblade @ 2005-09-14 20:00 UTC (permalink / raw) To: Jeff Dike; +Cc: user-mode-linux-devel On Wednesday 14 September 2005 21:22, Jeff Dike wrote: > On Tue, Sep 13, 2005 at 08:01:40PM +0200, Blaisorblade wrote: > > It's just because things are called under spinlocks and GFP_KERNEL is > > used - but if possible, it'd be better to use something better than > > GFP_ATOMIC (since this is performance critical). > This would be ubd_io_lock, which is taken for us by the block layer before > entering do_ubd_request. We could make that a GFP_ATOMIC allocation, > except that we have already dequeued the request, so would need to do > something with it if the allocation failed. > I'm wondering if we can drop the lock before do_io and pick it up > afterwards. The bitmap argument the COW bitmap, right? > is a global, which is a problem. Two > racing requests could result in one writing out a bitmap which is > either too old or too new. > So, I'm not sure how to handle this. We could requeue what's left of > the request if an allocation failure happens. Assuming it can be done, it'd be ok. However, why have we already dequeued the request? Looking for examples, via grep blkdev_dequeue_request drivers/ide/*.c and going opening drivers/ide/ide-io.c, I found blkdev_dequeue_request() called *after* end_that_request_first(), while there it's called before. A comment in blk_start_pre_flush() says there's some freedom, but probably leaving the request in the queue would be ok.... > We could drop the lock > and pick it up later, but we have to be careful to write out the > current bitmap, not one which we saved earlier or one which has been > updated to reflect a racing request which is coming through later. If you work on the second, be also sure to ask Jens Axboe (see MAINTAINERS for email) whether it's legal for the block layer. CC'ing him on the change in first place would not have been a bad idea, either (IMHO). > Jeff -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ___________________________________ Yahoo! Messenger: chiamate gratuite in tutto il mondo http://it.messenger.yahoo.com ------------------------------------------------------- SF.Net email is sponsored by: Tame your development challenges with Apache's Geronimo App Server. Download it for free - -and be entered to win a 42" plasma tv or your very own Sony(tm)PSP. Click here to play: http://sourceforge.net/geronimo.php _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [uml-devel] Re: "Sleeping in atomic section" with ubd aio patch 2005-09-14 20:00 ` Blaisorblade @ 2005-09-14 21:18 ` Jeff Dike 2005-09-16 19:20 ` Blaisorblade 0 siblings, 1 reply; 5+ messages in thread From: Jeff Dike @ 2005-09-14 21:18 UTC (permalink / raw) To: Blaisorblade; +Cc: user-mode-linux-devel On Wed, Sep 14, 2005 at 10:00:39PM +0200, Blaisorblade wrote: > Assuming it can be done, it'd be ok. > > However, why have we already dequeued the request? It is easier than removing segments from the request and finally dequeueing the request when it is finally empty. > Looking for examples, via grep blkdev_dequeue_request drivers/ide/*.c and > going opening drivers/ide/ide-io.c, I found blkdev_dequeue_request() called > *after* end_that_request_first(), while there it's called before. > > A comment in blk_start_pre_flush() says there's some freedom, but probably > leaving the request in the queue would be ok.... There is a good amount of freedom. The driver is given a set of requests, and has the job of making them happen. Jeff ------------------------------------------------------- SF.Net email is sponsored by: Tame your development challenges with Apache's Geronimo App Server. Download it for free - -and be entered to win a 42" plasma tv or your very own Sony(tm)PSP. Click here to play: http://sourceforge.net/geronimo.php _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [uml-devel] Re: "Sleeping in atomic section" with ubd aio patch 2005-09-14 21:18 ` Jeff Dike @ 2005-09-16 19:20 ` Blaisorblade 0 siblings, 0 replies; 5+ messages in thread From: Blaisorblade @ 2005-09-16 19:20 UTC (permalink / raw) To: Jeff Dike; +Cc: user-mode-linux-devel On Wednesday 14 September 2005 23:18, Jeff Dike wrote: > On Wed, Sep 14, 2005 at 10:00:39PM +0200, Blaisorblade wrote: > > Assuming it can be done, it'd be ok. > > > > However, why have we already dequeued the request? > > It is easier than removing segments from the request and finally > dequeueing the request when it is finally empty. Why can't you just move that exact call later, without removing segments? However, even if it's "easier" this way, IMHO it's still easier to defer the removal than to readd the thing into the queue (assuming the driver is supposed to do this). Not that I've looked well at the code or at the API recently. I'm busy with other stuff. > > Looking for examples, via grep blkdev_dequeue_request drivers/ide/*.c and > > going opening drivers/ide/ide-io.c, I found blkdev_dequeue_request() > > called *after* end_that_request_first(), while there it's called before. > > A comment in blk_start_pre_flush() says there's some freedom, but > > probably leaving the request in the queue would be ok.... > There is a good amount of freedom. The driver is given a set of > requests, and has the job of making them happen. > Jeff -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it ------------------------------------------------------- SF.Net email is sponsored by: Tame your development challenges with Apache's Geronimo App Server. Download it for free - -and be entered to win a 42" plasma tv or your very own Sony(tm)PSP. Click here to play: http://sourceforge.net/geronimo.php _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2005-09-16 19:22 UTC | newest] Thread overview: 5+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2005-09-13 18:01 [uml-devel] "Sleeping in atomic section" with ubd aio patch Blaisorblade 2005-09-14 19:22 ` [uml-devel] " Jeff Dike 2005-09-14 20:00 ` Blaisorblade 2005-09-14 21:18 ` Jeff Dike 2005-09-16 19:20 ` Blaisorblade
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