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From: bsuparna@in.ibm.com To: dprobes@oss.software.ibm.com, linux-kernel@vger.kernel.org Date: Thu, 18 Jan 2001 12:19:25 +0530 Subject: [ANNOUNCE] Dynamic Probes 1.3 released We've just released version 1.3 of the Dynamic Probes facility. This has 2.4.0 and 2.2.18 support and some bug fixes, including Andi Kleen's suggestions for fixing the races in handling of swapped out COW pages. For more information on DProbes see the dprobes homepage at http://oss.software.ibm.com/developer/opensource/linux/projects/dprobes/ Changes in this version: - DProbes for kernel version 2.2.18 and 2.4.0. - Fix for race condition in COW page handling and some other corrections in the detection of correct offsets in COW pages. - Removed the mmap_sem trylock from trap3 handling. The correct thing to do is to use the page_table_lock. - Probe on BOUND instruction now logs data. - Probes can now be inserted into modules that are getting initialized. - kernel/time.c and arch/i386/kernel/time.c treated as exclude regions. - Architecture specific FPU code moved to arch specific dprobes file. - Minor bug fix in merge code which merges probes that are excluded. - Exit to crashdump supported for 2.2.x kernels also. We are no longer updating the patches for 2.2.12, 2.2.16 on the site. If you require patches for these kernel versions, contact us at dprobes@oss.software.ibm.com ---------------------------------------------------------------------------------------------------------------------------------------------------------------- Race condition fixes in handling COW pages: ---------------------------------------------------------------- Some updates on the race condition fixes for COW page handling, since the discussions that happened last, for those who might have been following the thread: We eventually decided to drop the idea of trying achieve on-demand probe insertion for swapped out COW pages by having a vm_ops->swapin() routine that we could take over. The reason was that we realized that the vm_ops->swapin() replacement approach, while good for insert, is not suitable for remove, since then we might need to keep around the probes records for a removed module, until the swapped out pages eventually get cleaned out of the probes. (This may have been feasible without too much work because we already have the logic for quietly removing probes, but then it didn't seem like a good idea to have ghost records around in this way - makes it harder to maintain/debug ). So, we ended up implementing Andi Kleen's original suggestion of a 2 pass approach, instead. In the first pass, which takes place with the i_shared lock held, we build a list of swapped out page locators (mm, addr), while taking care of incrementing the mm reference count, and in the second pass which happens with the spin locks released, we actually bring in the page and cross-check that it is the same one that we'd meant to bring in. In the second pass, we hold the mmap_sem while bringing the page in. With David Miller's lock hierarchy fixes, the i_shared_lock is now always higher in the hierarchy than the page_table_lock, so we are OK there. I hope we haven't missed anything. If anyone spots any gotchas or slips, or some other races that still exist, do let us know. We've done some simple testing to try to exercise a few scenarios that we could simulate easily, but that's about it. Regards Suparna Suparna Bhattacharya Systems Software Group, IBM Global Services, India E-mail : bsuparna@in.ibm.com Phone : 91-80-5267117, Extn : 2525 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/