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62ed08422c
Several places in fd.c had badly-thought-through handling of error returns from lseek() and close(). The fact that those would seldom fail on valid FDs is probably the reason we've not noticed this up to now; but if they did fail, we'd get quite confused. LruDelete and LruInsert actually just Assert'd that lseek never fails, which is pretty awful on its face. In LruDelete, we indeed can't throw an error, because that's likely to get called during error abort and so throwing an error would probably just lead to an infinite loop. But by the same token, throwing an error from the close() right after that was ill-advised, not to mention that it would've left the LRU state corrupted since we'd already unlinked the VFD from the list. I also noticed that really, most of the time, we should know the current seek position and it shouldn't be necessary to do an lseek here at all. As patched, if we don't have a seek position and an lseek attempt doesn't give us one, we'll close the file but then subsequent re-open attempts will fail (except in the somewhat-unlikely case that a FileSeek(SEEK_SET) call comes between and allows us to re-establish a known target seek position). This isn't great but it won't result in any state corruption. Meanwhile, having an Assert instead of an honest test in LruInsert is really dangerous: if that lseek failed, a subsequent read or write would read or write from the start of the file, not where the caller expected, leading to data corruption. In both LruDelete and FileClose, if close() fails, just LOG that and mark the VFD closed anyway. Possibly leaking an FD is preferable to getting into an infinite loop or corrupting the VFD list. Besides, as far as I can tell from the POSIX spec, it's unspecified whether or not the file has been closed, so treating it as still open could be the wrong thing anyhow. I also fixed a number of other places that were being sloppy about behaving correctly when the seekPos is unknown. Also, I changed FileSeek to return -1 with EINVAL for the cases where it detects a bad offset, rather than throwing a hard elog(ERROR). It seemed pretty inconsistent that some bad-offset cases would get a failure return while others got elog(ERROR). It was missing an offset validity check for the SEEK_CUR case on a closed file, too. Back-patch to all supported branches, since all this code is fundamentally identical in all of them. Discussion: https://postgr.es/m/2982.1487617365@sss.pgh.pa.us |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.