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envelope-from=vsementsov@virtuozzo.com; helo=EUR05-DB8-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 06.04.2021 19:20, Vladimir Sementsov-Ogievskiy wrote: > 06.04.2021 18:51, Vladimir Sementsov-Ogievskiy wrote: >> If on nbd_close() we detach the thread (in >> nbd_co_establish_connection_cancel() thr->state becomes >> CONNECT_THREAD_RUNNING_DETACHED), after that point we should not use >> s->connect_thread (which is set to NULL), as running thread may free it >> at any time. >> >> Still nbd_co_establish_connection() does exactly this: it saves >> s->connect_thread to local variable (just for better code style) and >> use it even after yield point, when thread may be already detached. >> >> Fix that. Also check thr to be non-NULL on >> nbd_co_establish_connection() start for safety. >> >> After this patch "case CONNECT_THREAD_RUNNING_DETACHED" becomes >> impossible in the second switch in nbd_co_establish_connection(). >> Still, don't add extra abort() just before the release. If it somehow >> possible to reach this "case:" it won't hurt. Anyway, good refactoring >> of all this reconnect mess will come soon. >> >> Signed-off-by: Vladimir Sementsov-Ogievskiy >> --- >> >> Hi all! I faced a crash, just running 277 iotest in a loop. I can't >> reproduce it on master, it reproduces only on my branch with nbd >> reconnect refactorings. >> >> Still, it seems very possible that it may crash under some conditions. >> So I propose this patch for 6.0. It's written so that it's obvious that >> it will not hurt: >> >>   pre-patch, on first hunk we'll just crash if thr is NULL, >>   on second hunk it's safe to return -1, and using thr when >>   s->connect_thread is already zeroed is obviously wrong. > > Ha, occasionally I reinvented what Roman already does in "[PATCH 1/7] block/nbd: avoid touching freed connect_thread". > > My additional first hunk actually is not needed, as nbd_co_establish_connection is called after if (!nbd_clisent_connecting(s)) { return; }, so we should not be here after  nbd_co_establish_connection_cancel(bs, true); which is called with s->state set to NBD_CLIENT_QUIT. > > So, it would be more honest to take Roman's patch "[PATCH 1/7] block/nbd: avoid touching freed connect_thread" :) Still, I like my variant, because it make obvious that s->connect_thread may change only to NULL, not to some new pointer. > > Eric, could you take a look? If there no more pending block patches, I can try to send pull-request myself > Kevin, I see you've staged several patches for rc3.. This one is quite simple, could you add it too? -- Best regards, Vladimir