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b=RQcHWBex8iJgfrYary36U3cvf6PndC2aJCM0qFYEyJIAQsSVoSczn0zCb2y2gKfaz GEynYeJN7lHnAyLSBqYdMwwxEURPDwvhdEFVW+5a+oPuFji5nlFcCRbZAAeiFhWS3x wDufJth+Af4GWjMd2rfwU3elf968oZZdGTHNd+guPDk4fhmf4RlBrMbnLqB9n7bb43 HXKiavGri/bWX47oCYKVY20oMkjpSeiOsX2SjlAcr+YSBSISqxitBiN/wdrAWKwNWf hnlZWg0czt71yYQp54wpfHjOcDun5EkZnT7vXDEpaYx97JZbQPX83vZMWEGiMWBCdf LXXhjxqkq+Osg== From: Pratyush Yadav To: David Laight Cc: "'cel@kernel.org'" , Hugh Dickins , Christian Brauner , Al Viro , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "yukuai3@huawei.com" , "yangerkun@huaweicloud.com" , Chuck Lever , "stable@vger.kernel.org" , Jeff Layton , Yang Erkun Subject: Re: [PATCH v5 1/5] libfs: Return ENOSPC when the directory offset range is exhausted In-Reply-To: <95d0b9296e3f48ffb79a1de0b95f4726@AcuMS.aculab.com> (David Laight's message of "Sun, 15 Dec 2024 19:35:57 +0000") References: <20241215185816.1826975-1-cel@kernel.org> <20241215185816.1826975-2-cel@kernel.org> <95d0b9296e3f48ffb79a1de0b95f4726@AcuMS.aculab.com> Date: Mon, 16 Dec 2024 13:39:06 +0000 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 502684000C X-Rspam-User: X-Stat-Signature: xt3r17bkaqhoifbs8qziosxzo5ofbnjx X-HE-Tag: 1734356328-344333 X-HE-Meta: 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 H2ssBbuO gZqWTb/jv96zrL7U4xD/v780cD4Vau2H7c99jVyCdIT6T8Yravof4lnTGxEF0vRope+6N//4L11PNX4FSfV8+4iiDcBx6wfz/58688tMtQaKnYbIPS7sZ0BOYszPBoxoBv4iHtkwB2sGseJgApa1PU0cBd/GLj/wUhgYKumHaoD/VFUGyjCWIOAXoUZebp50tVu6HkdUOMHJ8qQmJ4nS+szxsk++Up2LSD8ii9nY1L8vOBnjUI/sGAccmNPBaNODtt094r9mehIQO68j64NbqEiF6nHFGyABHCaL5DE1lXM5DXjBybpP8nNPSC4xRlWTbSqHKw1D8UfqK5LnzUuQYoVOREA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Dec 15 2024, David Laight wrote: > From: cel@kernel.org >> Sent: 15 December 2024 18:58 >> >> From: Chuck Lever >> >> Testing shows that the EBUSY error return from mtree_alloc_cyclic() >> leaks into user space. The ERRORS section of "man creat(2)" says: >> >> > EBUSY O_EXCL was specified in flags and pathname refers >> > to a block device that is in use by the system >> > (e.g., it is mounted). >> >> ENOSPC is closer to what applications expect in this situation. >> >> Note that the normal range of simple directory offset values is >> 2..2^63, so hitting this error is going to be rare to impossible. >> >> Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets") >> Cc: # v6.9+ >> Reviewed-by: Jeff Layton >> Reviewed-by: Yang Erkun >> Signed-off-by: Chuck Lever >> --- >> fs/libfs.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/fs/libfs.c b/fs/libfs.c >> index 748ac5923154..f6d04c69f195 100644 >> --- a/fs/libfs.c >> +++ b/fs/libfs.c >> @@ -292,7 +292,9 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry) >> >> ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN, >> LONG_MAX, &octx->next_offset, GFP_KERNEL); >> - if (ret < 0) >> + if (unlikely(ret == -EBUSY)) >> + return -ENOSPC; >> + if (unlikely(ret < 0)) >> return ret; > > You've just added an extra comparison to a hot path. > Doing: > if (ret < 0) > return ret == -EBUSY ? -ENOSPC : ret; > would be better. This also has two comparisons: one for ret < 0 and another for ret == -EBUSY. So I don't see a difference. I was curious to see if compilers can somehow optimize one or the other, so I ran the two on godbolt and I see no real difference between the two: https://godbolt.org/z/9Gav6b6Mf -- Regards, Pratyush Yadav